Matrix-based intra prediction using filtering

ABSTRACT

Devices, systems and methods for digital video coding, which includes matrix-based intra prediction methods for video coding, are described. In a representative aspect, a method for video processing includes performing a conversion between a current video block of a video and a bitstream representation of the current video block using a matrix based intra prediction (MIP) mode in which a prediction block of the current video block is determined by performing, on reference boundary samples located to a left of the current video block and located to a top of the current video block, a boundary downsampling operation, followed by a matrix vector multiplication operation, and selectively followed by an upsampling operation, where instead of reduced boundary samples calculated from the reference boundary samples of the current video block in the boundary downsampling operation, the reference boundary samples are directly used for a prediction process in the upsampling operation.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Patent ApplicationNo. PCT/CN2020/088584, filed on May 5, 2020, which claims the priorityto and benefits of International Patent Application No.PCT/CN2019/085399, filed on May 1, 2019, and International PatentApplication No. PCT/CN2019/087047, filed on May 15, 2019. All theaforementioned patent applications are hereby incorporated by referencein their entireties.

TECHNICAL FIELD

This patent document relates to video coding techniques, devices andsystems.

BACKGROUND

In spite of the advances in video compression, digital video stillaccounts for the largest bandwidth use on the internet and other digitalcommunication networks. As the number of connected user devices capableof receiving and displaying video increases, it is expected that thebandwidth demand for digital video usage will continue to grow.

SUMMARY

Devices, systems and methods related to digital video coding, andspecifically, matrix-based intra prediction methods for video coding aredescribed. The described methods may be applied to both the existingvideo coding standards (e.g., High Efficiency Video Coding (HEVC)) andfuture video coding standards (e.g., Versatile Video Coding (VVC)) orcodecs.

A first example method for video processing includes performing aconversion between a current video block of a video and a bitstreamrepresentation of the current video block using a matrix based intraprediction (MIP) mode in which a prediction block of the current videoblock is determined by performing, on reference boundary samples locatedto a left of the current video block and located to a top of the currentvideo block, a boundary downsampling operation, followed by a matrixvector multiplication operation, and selectively followed by anupsampling operation, where instead of reduced boundary samplescalculated from the reference boundary samples of the current videoblock in the boundary downsampling operation, the reference boundarysamples are directly used for a prediction process in the upsamplingoperation.

A second example method for video processing includes performing, duringa conversion between a current video block of a video and a bitstreamrepresentation of the current video block, at least two filtering stageson samples of the current video block in an upsampling operationassociated with a matrix based intra prediction (MIP) mode in which aprediction block of the current video block is determined by performing,on previously coded samples of the video, a boundary downsamplingoperation, followed by a matrix vector multiplication operation, andselectively followed by the upsampling operation, where a firstprecision of the samples in a first filtering stage of the at least twofiltering stages is different from a second precision of the samples ina second filtering stage of the at least two filtering stages; andperforming the conversion between the current video block and thebitstream representation of the current video block.

A third example video encoding method includes encoding a current videoblock of a video using a matrix intra prediction (MIP) mode in which aprediction block of the current video block is determined by performing,on previously coded samples of the video, a boundary downsamplingoperation, followed by a matrix vector multiplication operation, andselectively followed by an upsampling operation; and adding, to a codedrepresentation of the current video block, a syntax element indicativeof applicability of the MIP mode to the current video block usingarithmetic coding in which a context for the syntax element is derivedbased on a rule.

A fourth example video decoding method includes parsing a codedrepresentation of a video comprising a current video block for a syntaxelement indicating whether the current video block is coded using amatrix intra prediction (MIP) mode, wherein the syntax element is codedusing arithmetic coding in which a context for the syntax element isderived based on a rule; and decoding the coded representation of thecurrent video block to generate a decoded current video block, whereinin a case that the current video block is coded using the MIP mode, thedecoding includes determining a prediction block of the current videoblock by performing, on previously coded samples of the video, aboundary downsampling operation, followed by a matrix vectormultiplication operation, and selectively followed by an upsamplingoperation.

In one representative aspect, the disclosed technology may be used toprovide a method for video processing. This exemplary method includesdetermining that a current video block is coded using an affine linearweighted intra prediction (ALWIP) mode, constructing, based on thedetermining, at least a portion of a most probable mode (MPM) list forthe ALWIP mode based on an at least a portion of an MPM list for anon-ALWIP intra mode, and performing, based on the MPM list for theALWIP mode, a conversion between the current video block and a bitstreamrepresentation of the current video block.

In another representative aspect, the disclosed technology may be usedto provide a method for video processing. This exemplary method includesdetermining that a luma component of a current video block is codedusing an affine linear weighted intra prediction (ALWIP) mode,inferring, based on the determining, a chroma intra mode, andperforming, based on the chroma intra mode, a conversion between thecurrent video block and a bitstream representation of the current videoblock.

In yet another representative aspect, the disclosed technology may beused to provide a method for video processing. This exemplary methodincludes determining that a current video block is coded using an affinelinear weighted intra prediction (ALWIP) mode, and performing, based onthe determining, a conversion between the current video block and abitstream representation of the current video block.

In yet another representative aspect, the disclosed technology may beused to provide a method for video processing. This exemplary methodincludes determining that a current video block is coded using a codingmode different from an affine linear weighted intra prediction (ALWIP)mode, and performing, based on the determining, a conversion between thecurrent video block and a bitstream representation of the current videoblock.

In yet another representative aspect, the disclosed technology may beused to provide a method for video processing. This exemplary methodincludes generating, for a current video block, a first prediction usingan affine linear weighted intra prediction (ALWIP) mode, generating,based on the first prediction, a second prediction using positiondependent intra prediction combination (PDPC), and performing, based onthe second prediction, a conversion between the current video block anda bitstream representation of the current video block.

In yet another representative aspect, the disclosed technology may beused to provide a method for video processing. This exemplary methodincludes determining that a current video block is coded using an affinelinear weighted intra prediction (ALWIP) mode, predicting, based on theALWIP mode, a plurality of sub-blocks of the current video block, andperforming, based on the predicting, a conversion between the currentvideo block and a bitstream representation of the current video block.

In yet another representative aspect, a method of video processing isdisclosed. The method includes determining, based on a rule for acurrent video block, a context of a flag indicative of use of affinelinear weighted intra prediction (ALWIP) mode during a conversionbetween the current video block and a bitstream representation of thecurrent video block, predicting, based on the ALWIP mode, a plurality ofsub-blocks of the current video block and performing, based on thepredicting, the conversion between the current video block and abitstream representation of the current video block.

In yet another representative aspect, a method of video processing isdisclosed. The method includes determining that a current video block iscoded using an affine linear weighted intra prediction (ALWIP) mode, andperforming, during a conversion between the current video block and abitstream representation of the current video block, at least twofiltering stages on samples of the current video block in an upsamplingprocess associated with the ALWIP mode, wherein a first precision of thesamples in a first filtering stage of the at least two filtering stagesis different from a second precision of the samples in a secondfiltering stage of the at least two filtering stages.

In yet another representative aspect, the above-described method isembodied in the form of processor-executable code and stored in acomputer-readable program medium.

In yet another representative aspect, a device that is configured oroperable to perform the above-described method is disclosed. The devicemay include a processor that is programmed to implement this method.

In yet another representative aspect, a video decoder apparatus mayimplement a method as described herein.

The above and other aspects and features of the disclosed technology aredescribed in greater detail in the drawings, the description and theclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of 33 intra prediction directions.

FIG. 2 shows an example of 67 intra prediction modes.

FIG. 3 shows an example of locations of samples used for the derivationof the weights of the linear model.

FIG. 4 shows an example of four reference lines neighboring a predictionblock.

FIG. 5A and FIG. 5B show examples of sub-partitions depending on blocksize.

FIG. 6 shows an example of ALWIP for 4×4 blocks.

FIG. 7 shows an example of ALWIP for 8×8 blocks.

FIG. 8 shows an example of ALWIP for 8×4 blocks.

FIG. 9 shows an example of ALWIP for 16×16 blocks.

FIG. 10 shows an example of neighboring blocks using in MPM listconstruction.

FIG. 11 shows a flowchart of an example method for matrix-based intraprediction, in accordance with the disclosed technology.

FIG. 12 shows a flowchart of another example method for matrix-basedintra prediction, in accordance with the disclosed technology.

FIG. 13 shows a flowchart of yet another example method for matrix-basedintra prediction, in accordance with the disclosed technology.

FIG. 14 shows a flowchart of yet another example method for matrix-basedintra prediction, in accordance with the disclosed technology.

FIG. 15 is a block diagram of an example of a hardware platform forimplementing a visual media decoding or a visual media encodingtechnique described in the present document.

FIG. 16 shows an example of neighboring blocks.

FIG. 17 is a block diagram that illustrates an example video codingsystem that may utilize the techniques of this disclosure.

FIG. 18 is a block diagram illustrating an example of video encoder.

FIG. 19 is a block diagram illustrating an example of video decoder.

FIG. 20 is a block diagram showing an example video processing system inwhich various techniques disclosed herein may be implemented.

FIGS. 21-24 describe example methods for matrix-based intra prediction,in accordance with the disclosed technology.

DETAILED DESCRIPTION

Due to the increasing demand of higher resolution video, video codingmethods and techniques are ubiquitous in modern technology. Video codecstypically include an electronic circuit or software that compresses ordecompresses digital video, and are continually being improved toprovide higher coding efficiency. A video codec converts uncompressedvideo to a compressed format or vice versa. There are complexrelationships between the video quality, the amount of data used torepresent the video (determined by the bit rate), the complexity of theencoding and decoding algorithms, sensitivity to data losses and errors,ease of editing, random access, and end-to-end delay (latency). Thecompressed format usually conforms to a standard video compressionspecification, e.g., the High Efficiency Video Coding (HEVC) standard(also known as H.265 or MPEG-H Part 2), the Versatile Video Coding (VVC)standard to be finalized, or other current and/or future video codingstandards.

Embodiments of the disclosed technology may be applied to existing videocoding standards (e.g., HEVC, H.265) and future standards to improveruntime performance. Section headings are used in the present documentto improve readability of the description and do not in any way limitthe discussion or the embodiments (and/or implementations) to therespective sections only.

1 A Brief Review on HEVC 1.1 Intra Prediction in HEVC/H.265

Intra prediction involves producing samples for a given TB (transformblock) using samples previously reconstructed in the considered colorchannel. The intra prediction mode is separately signaled for the lumaand chroma channels, with the chroma channel intra prediction modeoptionally dependent on the luma channel intra prediction mode via the‘DM_CHROMA’ mode. Although the intra prediction mode is signaled at thePB (prediction block) level, the intra prediction process is applied atthe TB level, in accordance with the residual quad-tree hierarchy forthe CU, thereby allowing the coding of one TB to have an effect on thecoding of the next TB within the CU, and therefore reducing the distanceto the samples used as reference values.

HEVC includes 35 intra prediction modes—a DC mode, a planar mode and 33directional, or ‘angular’ intra prediction modes. The 33 angular intraprediction modes are illustrated in FIG. 1.

For PBs associated with chroma color channels, the intra prediction modeis specified as either planar, DC, horizontal, vertical, ‘DM_CHROMA’mode or sometimes diagonal mode ‘34’.

Note for chroma formats 4:2:2 and 4:2:0, the chroma PB may overlap twoor four (respectively) luma PBs; in this case the luma direction forDM_CHROMA is taken from the top left of these luma PBs.

The DM_CHROMA mode indicates that the intra prediction mode of the lumacolor channel PB is applied to the chroma color channel PBs. Since thisis relatively common, the most-probable-mode coding scheme of theintra_chroma_pred_mode is biased in favor of this mode being selected.

2 Examples of Intra Prediction in VVC

2.1 Intra Mode Coding with 67 Intra Prediction Modes

To capture the arbitrary edge directions presented in natural video, thenumber of directional intra modes is extended from 33, as used in HEVC,to 65. The additional directional modes are depicted as red dottedarrows in FIG. 2, and the planar and DC modes remain the same. Thesedenser directional intra prediction modes apply for all block sizes andfor both luma and chroma intra predictions.

2.2 Examples of the Cross-Component Linear Model (CCLM)

In some embodiments, and to reduce the cross-component redundancy, across-component linear model (CCLM) prediction mode (also referred to asLM), is used in the JEM, for which the chroma samples are predictedbased on the reconstructed luma samples of the same CU by using a linearmodel as follows:

pred_(C)(i, j)=α·rec_(L)′(i, j)+β  (1)

Here, pred_(C)(i, j) represents the predicted chroma samples in a CU andrec_(L)′(i, j) represents the downsampled reconstructed luma samples ofthe same CU. Linear model parameter α and β are derived from therelation between luma values and chroma values from two samples, whichare luma sample with minimum sample value and with maximum sample insidethe set of downsampled neighboring luma samples, and their correspondingchroma samples. FIG. 3 shows an example of the location of the left andabove samples and the sample of the current block involved in the CCLMmode.

This parameter computation is performed as part of the decoding process,and is not just as an encoder search operation. As a result, no syntaxis used to convey the α and β values to the decoder.

For chroma intra mode coding, a total of 8 intra modes are allowed forchroma intra mode coding. Those modes include five traditional intramodes and three cross-component linear model modes (CCLM, LM_A, andLM_L). Chroma mode coding directly depends on the intra prediction modeof the corresponding luma block. Since separate block partitioningstructure for luma and chroma components is enabled in I slices, onechroma block may correspond to multiple luma blocks. Therefore, forChroma DM mode, the intra prediction mode of the corresponding lumablock covering the center position of the current chroma block isdirectly inherited.

2.3 Multiple Reference Line (MRL) Intra Prediction

Multiple reference line (MRL) intra prediction uses more reference linesfor intra prediction. In FIG. 4, an example of 4 reference lines isdepicted, where the samples of segments A and F are not fetched fromreconstructed neighboring samples but padded with the closest samplesfrom Segment B and E, respectively. HEVC intra-picture prediction usesthe nearest reference line (i.e., reference line 0). In MRL, 2additional lines (reference line 1 and reference line 3) are used. Theindex of selected reference line (mrl_idx) is signalled and used togenerate intra predictor. For reference line idx, which is greater than0, only include additional reference line modes in MPM list and onlysignal mpm index without remaining mode.

2.4 Intra Sub-Partitions (ISP)

The Intra Sub-Partitions (ISP) tool divides luma intra-predicted blocksvertically or horizontally into 2 or 4 sub-partitions depending on theblock size. For example, minimum block size for ISP is 4×8 (or 8×4). Ifblock size is greater than 4×8 (or 8×4) then the corresponding block isdivided by 4 sub-partitions. FIG. 5 shows examples of the twopossibilities. All sub-partitions fulfill the condition of having atleast 16 samples.

For each sub-partition, reconstructed samples are obtained by adding theresidual signal to the prediction signal. Here, a residual signal isgenerated by the processes such as entropy decoding, inversequantization and inverse transform. Therefore, the reconstructed samplevalues of each sub-partition are available to generate the prediction ofthe next sub-partition, and each sub-partition is processed repeatedly.In addition, the first sub-partition to be processed is the onecontaining the top-left sample of the CU and then continuing downwards(horizontal split) or rightwards (vertical split). As a result,reference samples used to generate the sub-partitions prediction signalsare only located at the left and above sides of the lines. Allsub-partitions share the same intra mode.

2.5 Affine Linear Weighted Intra Prediction (ALWIP or Matrix-Based IntraPrediction)

Affine linear weighted intra prediction (ALWIP, a.k.a. Matrix basedintra prediction (MIP)) is proposed in JVET-N0217.

In JVET-N0217, two tests are conducted. In test 1, ALWIP is designedwith a memory restriction of 8K bytes and at most 4 multiplications persample. Test 2 is similar to test 1, but further simplifies the designin terms of memory requirement and model architecture.

-   -   Single set of matrices and offset vectors for all block shapes.    -   Reduction of number of modes to 19 for all block shapes.    -   Reduction of memory requirement to 5760 10-bit values, that is        7.20 Kilobyte.    -   Linear interpolation of predicted samples is carried out in a        single step per direction replacing iterative interpolation as        in the first test.

2.5.1 Test 1 of JVET-N0217

For predicting the samples of a rectangular block of width W and heightH, affine linear weighted intra prediction (ALWIP) takes one line of Hreconstructed neighboring boundary samples left of the block and oneline of W reconstructed neighboring boundary samples above the block asinput. If the reconstructed samples are unavailable, they are generatedas it is done in the conventional intra prediction.

The generation of the prediction signal is based on the following threesteps:

Out of the boundary samples, four samples in the case of W=H=4 and eightsamples in all other cases are extracted by averaging.

A matrix vector multiplication, followed by addition of an offset, iscarried out with the averaged samples as an input. The result is areduced prediction signal on a subsampled set of samples in the originalblock.

The prediction signal at the remaining positions is generated from theprediction signal on the subsampled set by linear interpolation which isa single step linear interpolation in each direction.

The matrices and offset vectors needed to generate the prediction signalare taken from three sets S₀, S₁, S₂ of matrices. The set S₀ consists of18 matrices A₀ ^(i), i ∈ {0, . . . , 17} each of which has 16 rows and 4columns and 18 offset vectors b₀ ^(i), i ∈ {0, . . . , 17} each of size16. Matrices and offset vectors of that set are used for blocks of size4×4. The set S₁ consists of 10 matrices A₁ ^(i), i ∈ {0, . . . , 9},each of which has 16 rows and 8 columns and 10 offset vectors b₁ ^(i), i∈ {0, . . . , 9} each of size 16. Matrices and offset vectors of thatset are used for blocks of sizes 4×8, 8×4 and 8×8. Finally, the set S₂consists of 6 matrices A₂ ^(i), i ∈ {0, . . . , 5}, each of which has 64rows and 8 columns and of 6 offset vectors b₂ ^(i), i ∈ {0, . . . , 5}of size 64. Matrices and offset vectors of that set or parts of thesematrices and offset vectors are used for all other block-shapes.

The total number of multiplications needed in the computation of thematrix vector product is always smaller than or equal to 4×W×H. In otherwords, at most four multiplications per sample are required for theALWIP modes.

2.5.2 Averaging of the Boundary

In a first step, the input boundaries bdry^(top) and bdry^(left) arereduced to smaller boundaries bdry_(red) ^(top) and bdry_(red) ^(left).Here, bdry_(red) ^(top) and bdry_(red) ^(left) both consists of 2samples in the case of a 4×4-block and both consist of 4 samples in allother cases.

In the case of a 4×4-block, for 0≤i<2, one defines

$\begin{matrix}{{bdr{y_{red}^{top}\lbrack i\rbrack}} = {\left( {\left( {\sum\limits_{j = 0}^{1}{bdr{y^{top}\left\lbrack {{i \cdot 2} + j} \right\rbrack}}} \right) + 1} \right) ⪢ 1}} & \;\end{matrix}$

and defines bdry_(red) ^(left) analogously.

Otherwise, if the block-width W is given as W=4·2^(k), for 0≤i<4, onedefines

$\begin{matrix}{{bdr{y_{red}^{top}\lbrack i\rbrack}} = {\left( {\left( {\sum\limits_{j = 0}^{2^{k} - 1}{bdr{y^{top}\left\lbrack {{i \cdot 2^{k}} + j} \right\rbrack}}} \right) + \left( {1 ⪡ \left( {k - 1} \right)} \right)} \right) ⪢ k}} & \;\end{matrix}$

and defines bdry_(red) ^(left) analogously.

The two reduced boundaries bdry_(red) ^(top) and bdry_(red) ^(left) areconcatenated to a reduced boundary vector bdry_(red) which is thus ofsize four for blocks of shape 4×4 and of size eight for blocks of allother shapes. If mode refers to the ALWIP-mode, this concatenation isdefined as follows:

${bdry_{\tau ed}} = \left\{ \begin{matrix}\left\lbrack {{bdry_{red}^{top}}\ ,\ {bdry_{red}^{left}}} \right\rbrack & {{{for}\mspace{14mu} W} = {H = {{4\mspace{14mu}{and}\mspace{14mu}{mode}} < 18}}} \\\left\lbrack {{bdry_{red}^{left}},\ {bdry_{red}^{top}}} \right\rbrack & {{{for}\mspace{14mu} W} = {H = {{4\mspace{14mu}{and}\mspace{14mu}{mode}} \geq 18}}} \\\left\lbrack {{bdry_{red}^{top}}\ ,\ {bdry_{red}^{left}}} \right\rbrack & {{{for}\mspace{14mu}{\max\left( {W,H} \right)}} = {{8\mspace{13mu}{and}\mspace{14mu}{mode}} < 10}} \\\left\lbrack {{bdry_{red}^{left}},\ {bdry_{red}^{top}}} \right\rbrack & {{{for}\mspace{14mu}{\max\left( {W,H} \right)}} = {{8\mspace{9mu}{and}\mspace{14mu}{mode}} \geq 10}} \\\left\lbrack {{bdry_{red}^{top}}\ ,\ {bdry_{red}^{left}}} \right\rbrack & {{{for}\mspace{14mu}{\max\left( {W,H} \right)}} > {8\mspace{9mu}{and}\mspace{14mu}{mode}} < 6} \\\left\lbrack {{bdry_{red}^{left}},\ {bdry_{red}^{top}}} \right\rbrack & {{{for}\mspace{14mu}{\max\left( {W,H} \right)}} > {8\mspace{9mu}{and}\mspace{14mu}{mode}} \geq 6.}\end{matrix} \right.$

Finally, for the interpolation of the subsampled prediction signal, onlarge blocks a second version of the averaged boundary is needed.Namely, if min(W, H)>8 and W≥H, one writes W=8*2^(l), and, for 0≤i<8,defines

$\begin{matrix}{{bdr{y_{redII}^{top}\lbrack i\rbrack}} = {\left( {\left( {\sum\limits_{j = 0}^{2^{l} - 1}{bdr{y^{top}\left\lbrack {{i \cdot 2^{l}} + j} \right\rbrack}}} \right) + \left( {1 ⪡ \left( {l - 1} \right)} \right)} \right) ⪢ {l.}}} & \;\end{matrix}$

If min(W, H)>8 and H>W, one defines bdry_(redII) ^(left) analogously.

2.5.3 Generation of the Reduced Prediction Signal by Matrix VectorMultiplication

Out of the reduced input vector bdry_(red) one generates a reducedprediction signal pred_(red). The latter signal is a signal on thedownsampled block of width W_(red) and height H_(red). Here, W_(red) andH_(red) are defined as:

$W_{red} = \left\{ {{\begin{matrix}4 & {{{for}\mspace{14mu}{\max\left( {W,H} \right)}} \leq 8} \\{\min\left( {W,8} \right)} & {{{for}\mspace{14mu}{\max\left( {W,H} \right)}} > 8}\end{matrix}H_{red}} = \left\{ \begin{matrix}4 & {{{for}\mspace{14mu}{\max\left( {W,H} \right)}} \leq 8} \\{\min\left( {H,8} \right)} & {{{for}\mspace{14mu}{\max\left( {W,H} \right)}} > 8}\end{matrix} \right.} \right.$

The reduced prediction signal pred_(red) is computed by calculating amatrix vector product and adding an offset:

pred_(red) =A·bdry_(red) +b

Here, A is a matrix that has W_(red)·H_(red) rows and 4 columns if W=H=4and 8 columns in all other cases. b is a vector of size W_(red)·H_(red).

The matrix A and the vector b are taken from one of the sets S₀, S₁, S₂as follows. One defines an index idx=idx(W, H) as follows:

${id{x\left( {W,H} \right)}} = \left\{ {\begin{matrix}0 & {{{for}\mspace{14mu} W} = {H = 4}} \\1 & {{{for}\mspace{14mu}{\max\left( {W,H} \right)}} = 8} \\2 & {{{for}\mspace{14mu}{\max\left( {W,H} \right)}} > 8}\end{matrix}.} \right.$

Moreover, one puts m as follows:

$m = \left\{ {\begin{matrix}{mode} & {{{for}\mspace{14mu} W} = {H = {{4\ and\ mode} < {18}}}} \\{{mode} - 17} & {{{for}\mspace{14mu} W} = {H = {{4\ and\ mode} \geq {18}}}} \\{mode} & {{{for}\mspace{14mu}{\max\left( {W,H} \right)}} = {{8\ and\ mode} < {10}}} \\{{mode} - 9} & {{{for}\mspace{14mu}{\max\left( {W,H} \right)}} = {{8\ and\ mode} \geq {10}}} \\{mode} & {{{for}\mspace{14mu}{\max\left( {W,H} \right)}} > {8\ and\ mode} < 6} \\{{mode} - 5} & {{{for}\mspace{14mu}{\max\left( {W,H} \right)}} > {8\ and\ mode} \geq 6}\end{matrix}.} \right.$

Then, if idx≤1 or idx=2 and min(W, H)>4, one puts A=A_(idx) ^(m) andb=b_(idx) ^(m). In the case that idx=2 and min(W, H)=4, one lets A bethe matrix that arises by leaving out every row of A_(idx) ^(m) that, inthe case W=4, corresponds to an odd x-coordinate in the downsampledblock, or, in the case H=4, corresponds to an odd y-coordinate in thedownsampled block.

Finally, the reduced prediction signal is replaced by its transpose inthe following cases:

-   -   W=H=4and mode≥18    -   max(W, H)=8 and mode≥10    -   max(W, H)>8 and mode≥6

The number of multiplications required for calculation of pred_(red) is4 in the case of W=H=4 since in this case A has 4 columns and 16 rows.In all other cases, A has 8 columns and W_(red)·H_(red) rows and oneimmediately verifies that in these cases 8·W_(red)·H_(red)≤4·W·Hmultiplications are required, i.e. also in these cases, at most 4multiplications per sample are needed to compute pred_(red).

2.5.4 Illustration of the Entire ALWIP Process

The entire process of averaging, matrix vector multiplication and linearinterpolation is illustrated for different shapes in FIGS. 6-9. Note,that the remaining shapes are treated as in one of the depicted cases.

1. Given a 4×4 block, ALWIP takes two averages along each axis of theboundary. The resulting four input samples enter the matrix vectormultiplication. The matrices are taken from the set S₀. After adding anoffset, this yields the 16 final prediction samples. Linearinterpolation is not necessary for generating the prediction signal.Thus, a total of (4·16)/(4·4)=4 multiplications per sample areperformed.

2. Given an 8×8 block, ALWIP takes four averages along each axis of theboundary. The resulting eight input samples enter the matrix vectormultiplication. The matrices are taken from the set S₁. This yields 16samples on the odd positions of the prediction block. Thus, a total of(8·16)/(8·8)=2 multiplications per sample are performed. After adding anoffset, these samples are interpolated vertically by using the reducedtop boundary. Horizontal interpolation follows by using the originalleft boundary.

3. Given an 8×4 block, ALWIP takes four averages along the horizontalaxis of the boundary and the four original boundary values on the leftboundary. The resulting eight input samples enter the matrix vectormultiplication. The matrices are taken from the set S₁. This yields 16samples on the odd horizontal and each vertical positions of theprediction block. Thus, a total of (8·16)/(8·4)=4 multiplications persample are performed. After adding an offset, these samples areinterpolated horizontally by using the original left boundary.

4. Given a 16×16 block, ALWIP takes four averages along each axis of theboundary. The resulting eight input samples enter the matrix vectormultiplication. The matrices are taken from the set S₂. This yields 64samples on the odd positions of the prediction block. Thus, a total of(8·64)/(16·16)=2 multiplications per sample are performed. After addingan offset, these samples are interpolated vertically by using eightaverages of the top boundary. Horizontal interpolation follows by usingthe original left boundary. The interpolation process, in this case,does not add any multiplications. Therefore, totally, twomultiplications per sample are required to calculate ALWIP prediction.

For larger shapes, the procedure is essentially the same and it is easyto check that the number of multiplications per sample is less thanfour.

For W×8 blocks with W>8, only horizontal interpolation is necessary asthe samples are given at the odd horizontal and each vertical positions.

Finally for W×4 blocks with W>8, let A_kbe the matrix that arises byleaving out every row that corresponds to an odd entry along thehorizontal axis of the downsampled block. Thus, the output size is 32and again, only horizontal interpolation remains to be performed.

The transposed cases are treated accordingly.

2.5.5 Single Step Linear Interpolation

For a W×H block with max(W, H)≥8, the prediction signal arises from thereduced prediction signal pred_(red) on W_(red)×H_(red) by linearinterpolation. Depending on the block shape, linear interpolation isdone in vertical, horizontal or both directions. If linear interpolationis to be applied in both directions, it is first applied in horizontaldirection if W<H and it is first applied in vertical direction, else.

Consider without loss of generality a W×H block with max(W, H)≥8 andW≥H. Then, the one-dimensional linear interpolation is performed asfollows. Without loss of generality, it suffices to describe linearinterpolation in vertical direction. First, the reduced predictionsignal is extended to the top by the boundary signal. Define thevertical upsampling factor U_(ver)=H/H_(red) and write U_(ver)=2^(u)^(ver) >1. Then, define the extended reduced prediction signal by

$\begin{matrix}{{pre{{d_{red}\lbrack x\rbrack}\left\lbrack {- 1} \right\rbrack}} = \left\{ {\begin{matrix}{bdr{y_{red}^{top}\lbrack x\rbrack}} & {{{for}\mspace{14mu} W} = 8} \\{bdr{y_{redII}^{top}\lbrack x\rbrack}} & {{{for}\mspace{14mu} W} > 8}\end{matrix}.} \right.} & \;\end{matrix}$

Then, from this extended reduced prediction signal, the verticallylinear interpolated prediction signal is generated by

$\begin{matrix}{{pre{{d_{red}^{{ups},{ver}}\lbrack x\rbrack}\left\lbrack {{U_{ve\tau} \cdot y} + k} \right\rbrack}} = {\left( {{\left( {U_{ve\tau} - k - 1} \right) \cdot {{{pred}_{red}\lbrack x\rbrack}\left\lbrack {y - 1} \right\rbrack}} + {\left( {k + 1} \right) \cdot {{{pred}_{red}\lbrack x\rbrack}\lbrack y\rbrack}} + \frac{U_{ver}}{2}} \right) ⪢ u_{ver}}} & \;\end{matrix}$

for 0≤x<W_(red), 0≤y<H_(red) and 0≤k<U_(ver).

2.5.6 Signalization of the Proposed Intra Prediction Modes

For each Coding Unit (CU) in intra mode, a flag indicating if an ALWIPmode is to be applied on the corresponding Prediction Unit (PU) or notis sent in the bitstream. The signalization of the latter index isharmonized with MRL in the same way as in JVET-M0043. If an ALWIP modeis to be applied, the index predmode of the ALWIP mode is signaled usinga MPM-list with 3 MPMS.

Here, the derivation of the MPMs is performed using the intra-modes ofthe above and the left PU as follows. There are three fixed tablesmap_angular_to_alwip_(idx), idx ∈ {0, 1, 2} that assign to eachconventional intra prediction mode predmode_(Angular) an ALWIP mode

predmode_(ALWIP)=map_angular_to_alwip_(idx)[predmode_(Angular)].

For each PU of width W and height H one defines an index

idx(PU)=idx(W, H) ∈ {0, 1, 2}

that indicates from which of the three sets the ALWIP-parameters are tobe taken as in Section 2.5.3.

If the above Prediction Unit PU_(above) is available, belongs to thesame CTU as the current PU and is in intra mode, ifidx(PU)=idx(PU_(above)) and if ALWIP is applied on PU_(above) withALWIP-mode predmode_(ALWIP) ^(above), one puts

mode_(ALWIP) ^(above)=predmode_(ALWIP) ^(above).

If the above PU is available, belongs to the same CTU as the current PUand is in a intra mode and if a conventional intra prediction modepredmode_(Angular) ^(above) is applied on the above PU, one puts

mode_(ALWIP) ^(above)=map_angular_to_alwip_(idx(PU) _(above)₎[predmode_(Angular) ^(above)].

In all other cases, one puts

mode_(ALWIP) ^(above)=−1,

which means that this mode is unavailable. In the same way but withoutthe restriction that the left PU needs to belong to the same CTU as thecurrent PU, one derives a mode mode_(ALWIP) ^(left).

Finally, three fixed default lists list_(idx), idx ∈ {0, 1, 2} areprovided, each of which contains three distinct ALWIP modes. Out of thedefault list list_(idx(PU)) and the modes mode_(ALWIP) ^(above) andmode_(ALWIP) ^(left), one constructs three distinct MPMs by substituting−1 by default values as well as eliminating repetitions.

The left neighboring block and above neighboring block used in the ALWIPMPM list construction is A1 and B1 as shown in FIG. 10.

2.5.7 Adapted MPM-List Derivation for Conventional Luma and ChromaIntra-Prediction Modes

The proposed ALWIP-modes are harmonized with the MPM-based coding of theconventional intra-prediction modes as follows. The luma and chromaMPM-list derivation processes for the conventional intra-predictionmodes uses fixed tables map_alwip_to_angular_(idx), idx ∈ {0, 1, 2},mapping an ALWIP-mode predmode_(ALWIP) on a given PU to one of theconventional intra-prediction modes

predmode_(Angular)=map_alwip_to_angular_(idx(PU))[predmode_(ALWIP)]

For the luma MPM-list derivation, whenever a neighboring luma block isencountered which uses an ALWIP-mode predmode_(ALWIP), this block istreated as if it was using the conventional intra-prediction modepredmode_(Angular). For the chroma MPM-list derivation, whenever thecurrent luma block uses an LWIP-mode, the same mapping is used totranslate the ALWIP-mode to a conventional intra prediction mode.

2.5.8 Corresponding Modified Working Draft

In some embodiments, as described in this section, portions related tointra_lwip_flag, intra_lwip_mpm_flag, intra_lwip_mpm_idx andintra_lwip_mpm_remainder have been added to the working draft based onembodiments of the disclosed technology.

In some embodiments, as described in this section, the <begin> and <end>tags are used to denote additions and modifications to the working draftbased on embodiments of the disclosed technology.

Syntax tables Coding unit syntax coding_unit( x0, y0, cbWidth, cbHeight,treeType ) { Descriptor  if( tile_group_type != I | |sps_ibc_enabled_flag ) {   if( treeType != DUAL_TREE_CHROMA )   cu_skip_flag[ x0 ][ y0 ] ae(v)   if( cu_skip_flag[ x0 ][ y0 ] = = 0&& tile_group_type != I )    pred_mode_flag ae(v)   if( ( (tile_group_type = = I && cu_skip_flag[ x0 ][ y0 ] = = 0) | |    (tile_group_type != I && CuPredMode[ x0 ][ y0 ] != MODE_INTRA ) ) &&   sps_ibc_enabled_flag )    pred_mode_ibc_flag ae(v)  }  if(CuPredMode[ x0 ][ y0 ] = = MODE_INTRA ) {   if( sps_pcm_enabled_flag &&   cbWidth >= MinIpcmCbSizeY && cbWidth <= MaxIpcmCbSizeY &&   cbHeight >= MinIpcmCbSizeY && cbHeight <= MaxIpcmCbSizeY )   pcm_flag[ x0 ][ y0 ] ae(v)   if( pcm_flag[ x0 ][ y0 ] ) {    while(!byte_aligned( ) )     pcm_alignment_zero_bit f(1)    pcm_sample(cbWidth, cbHeight, treeType)   } else {    if( treeType = = SINGLE_TREE| | treeType = = DUAL_TREE_LUMA ) {     if( Abs( Log2( cbWidth ) - Log2(cbHeight ) ) <= 2)      intra_lwip_flag[ x0 ][ y0 ] ae(v)     if(intra_lwip_flag[ x0 ][ y0 ] ) {       intra_lwip_mpm_flag[ x0 ][ y0 ]ae(v)      if( intra_lwip_mpm_flag[ x0 ][ y0 ] )      intra_lwip_mpm_idx[ x0 ][ y0 ] ae(v)      else      intra_lwip_mpm_remainder[ x0 ][ y0 ] ae(v)     } else {      if( (y0 % CtbSizeY ) > 0)       intra_luma_ref_idx[ x0 ][ y0 ] ae(v)      if(intra_luma_ref_idx[ x0 ][ y0 ] = = 0 &&       ( cbWidth <= MaxTbSizeY || cbHeight <= MaxTbSizeY) &&       ( cbWidth * cbHeight > MinTbSizeY *MinTbSizeY ))       intra_subpartitions_mode_flag[ x0 ][ y0 ] ae(v)     if( intra_subpartitions_mode_flag[ x0 ][ y0 ] = = 1 &&      cbWidth <= MaxTbSizeY && cbHeight <= MaxTbSizeY)      intra_subpartitions_split_flag[ x0 ][ y0 ] ae(v)      if(intra_luma_ref_idx[ x0 ][ y0 ] = = 0 &&      intra_subpartitions_mode_flag[ x0 ][ y0 ] = = 0)      intra_luma_mpm_flag[ x0 ][ y0 ] ae(v)      if(intra_luma_mpm_flag[ x0 ][ y0 ] )       intra_luma_mpm_idx[ x0 ][ y0 ]ae(v)      else       intra_luma_mpm_remainder[ x0 ][ y0 ] ae(v)     }   }    if( treeType = = SINGLE_TREE | | treeType = = DUAL_TREE_CHROMA )    intra_chroma_pred_mode[ x0 ][ y0 ] ae(v)   }  } else if( treeType !=DUAL_TREE_CHROMA ) { /* MODE_INTER or MODE_IBC */   . . .

Semantics

<begin>intra_lwip_flag[x0][y0] equal to 1 specifies that the intraprediction type for luma samples is affine linear weighted intraprediction. intra_lwip_flag[x0][y0] equal to 0 specifies that the intraprediction type for luma samples is not affine linear weighted intraprediction.

When intra_lwip_flag[x0][y0] is not present, it is inferred to be equalto 0.

The syntax elements intra_lwip_mpm_flag[x0][y0],intra_lwip_mpm_idx[x0][y0] and intra_lwip_mpm_remainder [x0][y0] specifythe affine linear weighted intra prediction mode for luma samples. Thearray indices x0, y0 specify the location (x0, y0) of the top-left lumasample of the considered coding block relative to the top-left lumasample of the picture. When intra_lwip_mpm_flag[x0][y0] is equal to 1,the affine linear weighted intra prediction mode is inferred from aneighboring intra-predicted coding unit according to clause 8.4.X.

When intra_lwip_mpm_flag[x0][y0] is not present, it is inferred to beequal to 1.<end>

intra_subpartitions_split_flag[x0][y0] specifies whether the intrasubpartitions split type is horizontal or vertical. Whenintra_subpartitions_split_flag[x0][y0] is not present, it is inferred asfollows:

-   -   If intra_lwip_flag[x0][y0] is equal to 1,        intra_subpartitions_split_flag[x0][y0] is inferred to be equal        to 0.    -   Otherwise, the following applies:        -   If cbHeight is greater than MaxTbSizeY,            intra_subpartitions_split_flag[x0][y0] is inferred to be            equal to 0.        -   Otherwise (cbWidth is greater than MaxTbSizeY),            intra_subpartitions_split_flag[x0][y0] is inferred to be            equal to 1.

Decoding Process 8.4.1 General Decoding Process for Coding Units Codedin Intra Prediction Mode

Inputs to this process are:

-   -   a luma location (xCb, yCb) specifying the top-left sample of the        current coding block relative to the top-left luma sample of the        current picture,    -   a variable cbWidth specifying the width of the current coding        block in luma samples,    -   a variable cbHeight specifying the height of the current coding        block in luma samples,    -   a variable treeType specifying whether a single or a dual tree        is used and if a dual tree is used, it specifies whether the        current tree corresponds to the luma or chroma components.

Output of this process is a modified reconstructed picture beforein-loop filtering.

The derivation process for quantization parameters as specified inclause 8.7.1 is invoked with the luma location (xCb, yCb), the width ofthe current coding block in luma samples cbWidth and the height of thecurrent coding block in luma samples cbHeight, and the variable treeTypeas inputs.

When treeType is equal to SINGLE_TREE or treeType is equal toDUAL_TREE_LUMA, the decoding process for luma samples is specified asfollows:

-   -   If pcm_flag[xCb][yCb] is equal to 1, the reconstructed picture        is modified as follows:

S_(L)[xCb+i][yCb+j]=pcm_sample_luma[(cbHeight*j)+i]<<(BitDepth_(Y)−PcmBitDepth_(Y)),

with i=0 . . . cbWidth−1, j=0 . . . cbHeight−1   (8-6)

-   -   Otherwise, the following applies:        -   1. The luma intra prediction mode is derived as follows:            -   If intra_lwip_flag[xCb][yCb] is equal to 1, the                derivation process for the affine linear weighted intra                prediction mode as specified in clause 8.4.X is invoked                with the luma location (xCb, yCb), the width of the                current coding block in luma samples cbWidth and the                height of the current coding block in luma samples                cbHeight as input.            -   Otherwise, the derivation process for the luma intra                prediction mode as specified in clause 8.4.2 is invoked                with the luma location (xCb, yCb), the width of the                current coding block in luma samples cbWidth and the                height of the current coding block in luma samples                cbHeight as input.        -   2. The general decoding process for intra blocks as            specified in clause 8.4.4.1 is invoked with the luma            location (xCb, yCb), the tree type treeType, the variable            nTbW set equal to cbWidth, the variable nTbH set equal to            cbHeight, the variable predModeIntra set equal to            IntraPredModeY[xCb][yCb], and the variable cIdx set equal to            0 as inputs, and the output is a modified reconstructed            picture before in-loop filtering.

<begin>

8.4.X Derivation Process for Affine Linear Weighted Intra PredictionMode

Input to this process are:

-   -   a luma location (xCb, yCb) specifying the top-left sample of the        current luma coding block relative to the top-left luma sample        of the current picture,    -   a variable cbWidth specifying the width of the current coding        block in luma samples,    -   a variable cbHeight specifying the height of the current coding        block in luma samples.

In this process, the affine linear weighted intra prediction modeIntraPredModeY[xCb][yCb] is derived.

IntraPredModeY[xCb][yCb] is derived by the following ordered steps:

-   -   1. The neighboring locations (xNbA, yNbA) and (xNbB, yNbB) are        set equal to (xCb−1, yCb) and (xCb, yCb−1), respectively.    -   2. For X being replaced by either A or B, the variables        candLwipModeX are derived as follows:        -   The availability derivation process for a block as specified            in clause 6.4.X [Ed. (BB): Neighboring blocks availability            checking process tbd] is invoked with the location (xCurr,            yCurr) set equal to (xCb, yCb) and the neighboring location            (xNbY, yNbY) set equal to (xNbX, yNbX) as inputs, and the            output is assigned to availableX.        -   The candidate affine linear weighted intra prediction mode            candLwipModeX is derived as follows:            -   If one or more of the following conditions are true,                candLwipModeX is set equal to −1.                -   The variable availableX is equal to FALSE.                -   CuPredMode[xNbX][yNbX] is not equal to MODE_INTRA                    and mh_intra_flag[xNbX][yNbX] is not equal to 1.                -   pcm_flag[xNbX][yNbX] is equal to 1.                -   X is equal to B and yCb−1 is less than ((yCb>>Ctb                    Log 2SizeY)<<Ctb Log 2SizeY).            -   Otherwise, the following applies:                -   The size type derivation process for a block as                    specified in clause 8.4.X.1 is invoked with the                    width of the current coding block in luma samples                    cbWidth and the height of the current coding block                    in luma samples cbHeight as input, and the output is                    assigned to variable sizeId.                -   If intra_lwip_flag[xNbX][yNbX] is equal to 1, the                    size type derivation process for a block as                    specified in clause 8.4.X.1 is invoked with the                    width of the neighboring coding block in luma                    samples nbWidthX and the height of the neighboring                    coding block in luma samples nbHeightX as input, and                    the output is assigned to variable sizeIdX.                -    If sizeId is equal to sizeIdX, candLwipModeX is set                    equal to IntraPredModeY[xNbX][yNbX].                -    Otherwise, candLwipModeX is set equal to −1.                -   Otherwise, candLwipModeX is derived using                    IntraPredModeY[xNbX][yNbX] and sizeId as specified                    in Table 8-X1.    -   3. The candLwipModeList[x] with x=0 . . . 2 is derived as        follows, using lwipMpmCand[sizeId] as specified in Table 8-X2:        -   If candLwipModeA and candLwipModeB are both equal to −1, the            following applies:

candLwipModeList[0]=lwipMpmCand[sizeId][0]  (8-X1)

candLwipModeList[1]=lwipMpmCand[sizeId][1]  (8-X2)

candLwipModeList[2]=lwipMpmCand[sizeId][2]  (8-X3)

-   -   -   Otherwise, the following applies:            -   If candLwipModeA is equal to candLwipModeB or if either                candLwipModeA or candLwipModeB is equal to −1, the                following applies:

candLwipModeList[0]=(candLwipModeA !=−1) ? candLwipModeA:candLwipModeB  (8-X4)

-   -   -   -   -   If candLwipModeList[0] is equal to                    lwipMpmCand[sizeId][0], the following applies:

candLwipModeList[1]=lwipMpmCand[sizeId][1]  (8-X5)

candLwipModeList[2]=lwipMpmCand[sizeId][2]  (8-X6)

-   -   -   -   -   Otherwise, the following applies:

candLwipModeList[1]=lwipMpmCand[sizeId][0]  (8-X7)

candLwipModeList[2]=(candLwipModeList[0] !=lwipMpmCand[sizeId][1]) ?lwipMpmCand[sizeId][1]:lwipMpmCand[sizeId][2]  (8-X8)

-   -   -   -   Otherwise, the following applies:

candLwipModeList[0]=candLwipModeA   (8-X9)

candLwipModeList[1]=candLwipModeB   (8-X10)

-   -   -   -   -   If candLwipModeA and candLwipModeB are both not                    equal to lwipMpmCand[sizeId][0], the following                    applies:

candLwipModeList[2]=lwipMpmCand[sizeId][0]  (8-X11)

-   -   -   -   -   Otherwise, the following applies:                -    If candLwipModeA and candLwipModeB are both not                    equal to lwipMpmCand[sizeId][1], the following                    applies:

candLwipModeList[2]=lwipMpmCand[sizeId][1]  (8-X12)

-   -   -   -   -    Otherwise, the following applies:

candLwipModeList[2]=lwipMpmCand[sizeId][2]  (8-X13)

-   -   4. IntraPredModeY[xCb][yCb] is derived by applying the following        procedure:        -   If intra_lwip_mpm_flag[xCb][yCb] is equal to 1, the            IntraPredModeY[xCb][yCb] is set equal to            candLwipModeList[intra_lwip_mpm_idx[xCb][yCb]].        -   Otherwise, IntraPredModeY[xCb][yCb] is derived by applying            the following ordered steps:            -   1. When candLwipModeList[i] is greater than                candLwipModeList[j] for i=0 . . . 1 and for each i,                j=(i+1) . . . 2, both values are swapped as follows:

(candLwipModeList[i], candLwipModeList[j])=Swap(candLwipModeList[i],candLwipModeList[j])   (8-X14)

-   -   -   -   2. IntraPredModeY[xCb][yCb] is derived by the following                ordered steps:                -   i. IntraPredModeY[xCb][yCb] is set equal to                    intra_lwip_mpm_remainder[xCb][yCb].                -   ii. For i equal to 0 to 2, inclusive, when                    IntraPredModeY[xCb][yCb] is greater than or equal to                    candLwipModeList[i], the value of                    IntraPredModeY[xCb][yCb] is incremented by one.

The variable IntraPredModeY[x][y] with x=xCb . . . xCb+cbWidth−1 andy=yCb . . . yCb+cbHeight−1 is set to be equal toIntraPredModeY[xCb][yCb].

8.4.X.1 Derivation Process for Prediction Block Size Type

Input to this process are:

-   -   a variable cbWidth specifying the width of the current coding        block in luma samples,    -   a variable cbHeight specifying the height of the current coding        block in luma samples.

Output of this process is a variable sizeId.

The variable sizeId is derived as follows:

-   -   If both cbWidth and cbHeight are equal to 4, sizeId is set equal        to 0.    -   Otherwise, if both cbWidth and cbHeight are less than or equal        to 8, sizeId is set equal to 1.    -   Otherwise, sizeId is set equal to 2.

TABLE 8-X1 Specification of mapping between intra prediction and affinelinear weighted intra prediction modes block size type sizeldIntraPredModeY[ xNbX ][ yNbX ] 0 1 2  0 17  0  5  1 17  0  1  2, 3 17 10 3  4, 5  9 10  3  6, 7  9 10  3  8, 9  9 10  3 10, 11  9 10  0 12, 1317  4  0 14, 15 17  6  0 16, 17 17  7  4 18, 19 17  7  4 20, 21 17  7  422, 23 17  5  5 24, 25 17  5  1 26, 27  5  0  1 28, 29  5  0  1 30, 31 5  3  1 32, 33  5  3  1 34, 35 34 12  6 36, 37 22 12  6 38, 39 22 12  640, 41 22 12  6 42, 43 22 14  6 44, 45 34 14 10 46, 47 34 14 10 48, 4934 16  9 50, 51 34 16  9 52, 53 34 16  9 54, 55 34 15  9 56, 57 34 13  958, 59 26  1  8 60, 61 26  1  8 62, 63 26  1  8 64, 65 26  1  8 66 26  1 8

TABLE 8-X2 Specification of affine linear weighted intra predictioncandidate modes candidate mode 0 1 2 IwipMpmCand[ 0 ] 17 34  5IwipMpmCand[ 1 ]  0  7 16 IwipMpmCand[ 2 ]  1  4  6

<end>

8.4.2. Derivation Process for Luma Intra Prediction Mode

Input to this process are:

-   -   a luma location (xCb, yCb) specifying the top-left sample of the        current luma coding block relative to the top-left luma sample        of the current picture,    -   a variable cbWidth specifying the width of the current coding        block in luma samples,    -   a variable cbHeight specifying the height of the current coding        block in luma samples.

In this process, the luma intra prediction mode IntraPredModeY[xCb][yCb]is derived.

Table 8-1 specifies the value for the intra prediction modeIntraPredModeY[xCb][yCb] and the associated names.

TABLE 8-1 Specification of intro prediction mode and associated namesIntro prediction mode Associated name 0 INTRA_PLANAR 1 INTRA_DC 2..66INTRA_ANGULAR2..INTRA_ANGULAR66 81..83 INTRA_LT_CCLM, INTRA_L_CCLM,INTRA_T_CCLM NOTE - : The intra prediction modes INTRA_LT_CCLM,INTRA_L_CCLM and INTRA_T_CCLM are only applicable to chroma components.

IntraPredModeY[xCb][yCb] is derived by the following ordered steps:

-   -   1. The neighboring locations (xNbA, yNbA) and (xNbB, yNbB) are        set equal to (xCb−1, yCb+cbHeight−1) and (xCb+cbWidth−1, yCb−1),        respectively.    -   2. For X being replaced by either A or B, the variables        candIntraPredModeX are derived as follows:        -   The availability derivation process for a block as specified            in clause <begin>6.4.X [Ed. (BB): Neighboring blocks            availability checking process tbd] <end>is invoked with the            location (xCurr, yCurr) set equal to (xCb, yCb) and the            neighboring location (xNbY, yNbY) set equal to (xNbX, yNbX)            as inputs, and the output is assigned to availableX.        -   The candidate intra prediction mode candIntraPredModeX is            derived as follows:            -   If one or more of the following conditions are true,                candIntraPredModeX is set equal to INTRA_PLANAR.                -   The variable availableX is equal to FALSE.                -   CuPredMode[xNbX][yNbX] is not equal to MODE_INTRA                    and clip_flag[xNbX][yNbX] is not equal to 1.                -   pcm_flag[xNbX][yNbX] is equal to 1.                -   X is equal to B and yCb−1 is less than ((yCb>>Ctb                    Log 2SizeY)<<Ctb Log 2SizeY).            -   Otherwise, candIntraPredModeX is derived as follows:                -   If intra_lwip_flag[xCb][yCb] is equal to 1,                    candIntraPredModeX is derived by the following                    ordered steps:                -    i. The size type derivation process for a block as                    specified in clause 8.4.X.1 is invoked with the                    width of the current coding block in luma samples                    cbWidth and the height of the current coding block                    in luma samples cbHeight as input, and the output is                    assigned to variable sizeId.                -    ii. candIntraPredModeX is derived using                    IntraPredModeY[xNbX][yNbX] and sizeId as specified                    in Table 8-X3.            -   Otherwise, candIntraPredModeX is set equal to                IntraPredModeY[xNbX][yNbX].    -   3. The variables ispDefaultMode1 and ispDefaultMode2 are defined        as follows:        -   If IntraSubPartitionsSplitType is equal to ISP_HOR_SPLIT,            ispDefaultMode1 is set equal to INTRA_ANGULAR18 and            ispDefaultMode2 is set equal to INTRA_ANGULAR5.        -   Otherwise, ispDefaultMode1 is set equal to INTRA_ANGULAR50            and ispDefaultMode2 is set equal to INTRA_ANGULAR63.

TABLE 8-X3 Specification of mapping between affine linear weighted intraprediction and intra prediction modes block size type sizeIdIntraPredModeY[ xNbX ][ yNbX ] 0 1 2  0  0  0  1  1 18  1  1  2 18  0  1 3  0  1  1  4 18  0 18  5  0 22  0  6 12 18  1  7  0 18  0  8 18  1  1 9  2  0 50 10 18  1  0 11 12  0 12 18  1 13 18  0 14  1 44 15 18  0 1618 50 17  0  1 18  0  0 19 50 20  0 21 50 22  0 23 56 24  0 25 50 26 6627 50 28 56 29 50 30 50 31  1 32 50 33 50 34 50

8.4.3 Derivation Process for Chroma Intra Prediction Mode

Input to this process are:

-   -   a luma location (xCb, yCb) specifying the top-left sample of the        current chroma coding block relative to the top-left luma sample        of the current picture,    -   a variable cbWidth specifying the width of the current coding        block in luma samples,    -   a variable cbHeight specifying the height of the current coding        block in luma samples.

In this process, the chroma intra prediction modeIntraPredModeC[xCb][yCb] is derived.

The corresponding luma intra prediction mode lumaIntraPredMode isderived as follows:

-   -   If intra_lwip_flag[xCb][yCb] is equal to 1, lumaIntraPredMode is        derived by the following ordered steps:        -   i. The size type derivation process for a block as specified            in clause 8.4.X.1 is invoked with the width of the current            coding block in luma samples cbWidth and the height of the            current coding block in luma samples cbHeight as input, and            the output is assigned to variable sizeId.        -   ii. The luma intra prediction mode is derived using            IntraPredModeY[xCb+cbWidth/2][yCb+cbHeight/2] and sizeId as            specified in Table 8-X3 and assigning the value of            candIntraPredModeX to lumaIntraPredMode.    -   Otherwise, lumaIntraPredMode is set equal to        IntraPredModeY[xCb+cbWidth/2][yCb+cbHeight/2].

The chroma intra prediction mode IntraPredModeC[xCb][yCb] is derivedusing intra_chroma_pred_mode[xCb][yCb] and lumaIntraPredMode asspecified in Table 8-2 and Table 8-3.

xxx. Intra Sample Prediction

<begin>

Inputs to this process are:

-   -   a sample location (xTbCmp, yTbCmp) specifying the top-left        sample of the current transform block relative to the top-left        sample of the current picture,    -   a variable predModeIntra specifying the intra prediction mode,    -   a variable nTbW specifying the transform block width,    -   a variable nTbH specifying the transform block height,    -   a variable nCbW specifying the coding block width,    -   a variable nCbH specifying the coding block height,    -   a variable cIdx specifying the colour component of the current        block.

Outputs of this process are the predicted samples predSamples[x][y],with x=0 . . . nTbW−1, y=0 . . . nTbH−1.

The predicted samples predSamples[x][y] are derived as follows:

-   -   If intra_lwip_flag[xTbCmp][yTbCmp] is equal to 1 and cIdx is        equal to 0, the affine linear weighted intra sample prediction        process as specified in clause 8.4.4.2.X1 is invoked with the        location (xTbCmp, yTbCmp), the intra prediction mode        predModeIntra, the transform block width nTbW and height nTbH as        inputs, and the output is predSamples.    -   Otherwise, the general intra sample prediction process as        specified in clause 8.4.4.2.X1. is invoked with the location        (xTbCmp, yTbCmp), the intra prediction mode predModeIntra, the        transform block width nTbW and height nTbH, the coding block        width nCbW and height nCbH, and the variable cIdx as inputs, and        the output is predSamples.

8.4.4.2.X1 Affine Linear Weighted Intra Sample Prediction

Inputs to this process are:

-   -   a sample location (xTbCmp, yTbCmp) specifying the top-left        sample of the current transform block relative to the top-left        sample of the current picture,    -   a variable predModeIntra specifying the intra prediction mode,    -   a variable nTbW specifying the transform block width,    -   a variable nTbH specifying the transform block height.

Outputs of this process are the predicted samples predSamples[x][y],with x=0 . . . nTbW−1, y=0 . . . nTbH−1.

The size type derivation process for a block as specified in clause8.4.X.1 is invoked with the transform block width nTbW and the transformblock height nTbH as input, and the output is assigned to variablesizeId.

Variables numModes, boundarySize, predW, predH and predC are derivedusing sizeId as specified in Table 8-X4.

TABLE 8-X4 Specification of number of modes, boundary sample size andprediction sizes depending on sizeId sizeId numModes boundarySize predWpredH predC 0 35 2 4 4 4 1 19 4 4 4 4 2 11 4 Min( Min( 8 nTbW, 8 ) nTbH,8 )

The flag isTransposed is derived as follows:

isTransposed=(predModeIntra>(numModes/2)) ? 1:0   (8-X15)

The flags needUpsBdryHor and needUpsBdryVer are derived as follows:

needUpsBdryHor=(nTbW>predW) ? TRUE:FALSE   (8-X16)

needUpsBdryVer=(nTbH>predH) ? TRUE:FALSE   (8-X17)

The variables upsBdryW and upsBdryH are derived as follows:

upsBdryW=(nTbH>nTbW) ? nTbW:predW   (8-X18)

upsBdryH=(nTbH>nTbW) ? predH:nTbH   (8-X19)

The variables lwipW and lwipH are derived as follows:

lwipW=(isTransposed==1) ? predH:predW   (8-X20)

lwipH=(isTransposed==1) ? predW:predH   (8-X21)

For the generation of the reference samples refT[x] with x=0 . . .nTbW−1 and refL[y] with y=0 . . . nTbH−1, the reference samplederivation process as specified in clause 8.4.4.2.X2 is invoked with thesample location (xTbCmp, yTbCmp), the transform block width nTbW, thetransform block height nTbH as inputs, and top and left referencesamples refT[x] with x=0 . . . nTbW−1 and refL[y] with y=0 . . . nTbH−1,respectively, as outputs.

For the generation of the boundary samples p[x] with x=0 . . .2*boundarySize−1, the following applies:

-   -   The boundary reduction process as specified in clause 8.4.4.2.X3        is invoked for the top reference samples with the block size        nTbW, the reference samples refT, the boundary size        boundarySize, the upsampling boundary flag needUpsBdryVer, and        the upsampling boundary size upsBdryW as inputs, and reduced        boundary samples redT[x] with x=0 . . . boundarySize−1 and        upsampling boundary samples upsBdryT[x] with x=0 . . .        upsBdryW−1 as outputs.    -   The boundary reduction process as specified in clause 8.4.4.2.X3        is invoked for the left reference samples with the block size        nTbH, the reference samples refL, the boundary size        boundarySize, the upsampling boundary flag needUpsBdryHor, and        the upsampling boundary size upsBdryH as inputs, and reduced        boundary samples redL[x] with x=0 . . . boundarySize−1 and        upsampling boundary samples upsBdryL[x] with x=0 . . .        upsBdryH−1 as outputs.    -   The reduced top and left boundary samples redT and redL are        assigned to the boundary sample array p as follows:        -   If isTransposed is equal to 1, p[x] is set equal to redL[x]            with x=0 . . . boundarySize−1 and p[x+boundarySize] is set            equal to redT[x] with x=0 . . . boundarySize−1.        -   Otherwise, p[x] is set equal to redT[x] with x=0 . . .            boundarySize−1 and p[x+boundarySize] is set equal to redL[x]            with x=0 . . . boundarySize−1.

For the intra sample prediction process according to predModeIntra, thefollowing ordered steps apply:

-   -   1. The affine linear weighted samples predLwip[x][y], with x=0 .        . . lwipW−1, y=0 . . . lwipH−1 are derived as follows:        -   The variable modeId is derived as follows:

modeId=predModeIntra−(isTransposed==1) ? (numModes/2):0   (8-X22)

-   -   -   The weight matrix mWeight[x][y] with x=0 . . .            2*boundarySize−1, y=0 . . . predC*predC−1 is derived using            sizeId and modeId as specified in Table 8-XX [TBD: add            weight matrices].        -   The bias vector vBias[y] with y=0 . . . predC*predC−1 is            derived using sizeId and modeId as specified in Table 8-XX            [TBD: add bias vectors].        -   The variable sW is derived using sizeId and modeId as            specified in Table 8-X5.        -   The affine linear weighted samples predLwip[x][y], with x=0            . . . lwipW−1, y=0 . . . lwipH−1 are derived as follows:

oW=1<<(sW−1)   (8-X23)

sB=BitDepth_(Y)−1   (8-X24)

incW=(predC>lwipW) ? 2:1   (8-X25)

incH=(predC>lwipH) ? 2:1   (8-X26)

predLwip[x][y]=((Σ_(i=0) ^(2*boundarySize−1)mWeight[i][y*incH*predC+x*incW]*p[i])+(vBias[y*incH*predC+x*incW]<<sB)+oW)>>sW  (8-X27)

-   -   2. The predicted samples predSamples[x][y], with x=0 . . .        nTbW−1, y=0 . . . nTbH−1 are derived as follows:        -   When isTransposed is equal to 1, predLwip[x][y], with x=0 .            . . predW−1, y=0 . . . predH−1 is set equal to            predLwip[y][x].        -   If needUpsBdryVer is equal to TRUE or needUpsBdryHor is            equal to TRUE, the prediction upsampling process as            specified in clause 8.4.4.2.X4 is invoked with the input            block width predW, the input block height predH, affine            linear weighted samples predLwip, the transform block width            nTbW, the transform block height nTbH, the upsampling            boundary width upsBdryW, the upsampling boundary height            upsBdryH, the top upsampling boundary samples upsBdryT, and            the left upsampling boundary samples upsBdryL as inputs, and            the output is the predicted sample array predSamples.        -   Otherwise, predSamples[x][y], with x=0 . . . nTbW−1, y=0 . .            . nTbH−1 is set equal to predLwip[x][y].

TABLE 8-X5 Specification of weight shifts SW depending on sizeId andmodeId modeId sizeId 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 0 8 8 88 8 8 8 8 8 8 8 8 8 8 8 8 8 8 1 8 8 8 9 8 8 8 8 9 8 2 8 8 8 8 8 8

8.4.4.2.X2 Reference Sample Derivation Process

Inputs to this process are:

-   -   a sample location (xTbY, yTbY) specifying the top-left luma        sample of the current transform block relative to the top-left        luma sample of the current picture,    -   a variable nTbW specifying the transform block width,    -   a variable nTbH specifying the transform block height.

Outputs of this process are the top and left reference samples refT[x]with x=0 . . . nTbW−1 and refL[y] with y=0 . . . nTbH−1, respectively.

The neighboring samples refT[x] with x=0 . . . nTbW−1 and refL[y] withy=0 . . . nTbH−1 are constructed samples prior to the in-loop filterprocess and derived as follows:

-   -   The top and left neighboring luma locations (xNbT, yNbT) and        (xNbL, yNbL) are specified by:

(xNbT, yNbT)=(xTbY+x, yTbY−1)   (8-X28)

(xNbL, yNbL)=(xTbY−1, yTbY+y)   (8-X29)

-   -   The availability derivation process for a block as specified in        clause 6.4.X [Ed. (BB): Neighboring blocks availability checking        process tbd] is invoked with the current luma location (xCurr,        yCurr) set equal to (xTbY, yTbY) and the top neighboring luma        location (xNbT, yNbT) as inputs, and the output is assigned to        availTop[x] with x=0 . . . nTbW−1.    -   The availability derivation process for a block as specified in        clause 6.4.X [Ed. (BB): Neighboring blocks availability checking        process tbd] is invoked with the current luma location (xCurr,        yCurr) set equal to (xTbY, yTbY) and the left neighboring luma        location (xNbL, yNbL) as inputs, and the output is assigned to        availLeft[y] with y=0 . . . nTbH−1.    -   The top reference samples refT[x] with x=0 . . . nTbW−1 are        derived as follows:        -   If all availTop[x] with x=0 . . . nTbW−1 are equal to TRUE,            the sample at the location (xNbT, yNbT) is assigned to            refT[x] with x=0 . . . nTbW−1.        -   Otherwise, if availTop[0] is equal to FALSE, all refT[x]            with x=0 . . . nTbW−1 are set equal to 1<<(BitDepth_(Y)−1).        -   Otherwise, reference samples refT[x] with x=0 . . . nTbW−1            are derived by the following ordered steps:            -   1. The variable lastT is set equal to the position x of                the first element in the sequence availTop[x] with x=1 .                . . nTbW−1 that is equal to FALSE.            -   2. For every x=0 . . . lastT−1, the sample at the                location (xNbT, yNbT) is assigned to refT[x].            -   3. For every x=lastT . . . nTbW−1, refT[x] is set equal                to refT[lastT−1].    -   The left reference samples refL[y] with x=0 . . . nTbH−1 are        derived as follows:        -   If all availLeft[y] with y=0 . . . nTbH−1 are equal to TRUE,            the sample at the location (xNbL, yNbL) is assigned to            refL[y] with y=0 . . . nTbH−1.        -   Otherwise, if availLeft[0] is equal to FALSE, all refL[y]            with y=0 . . . nTbH−1 are set equal to 1<<(BitDepth_(Y)−1).        -   Otherwise, reference samples refL[y] with y=0 . . . nTbH−1            are derived by the following ordered steps:            -   1. The variable lastL is set equal to the position y of                the first element in the sequence availLeft[y] with y=1                . . . nTbH−1 that is equal to FALSE.            -   2. For every y=0 . . . lastL−1, the sample at the                location (xNbL, yNbL) is assigned to refL[y].            -   3. For every y=lastL . . . nTbH−1, refL[y] is set equal                to refL[lastL−1].

Specification of the Boundary Reduction Process

Inputs to this process are:

-   -   a variable nTbX specifying the transform block size,    -   reference samples refX[x] with x=0 . . . nTbX−1,    -   a variable boundarySize specifying the downsampled boundary        size,    -   a flag needUpsBdryX specifying whether intermediate boundary        samples are required for upsampling,    -   a variable upsBdrySize specifying the boundary size for        upsampling.

Outputs of this process are the reduced boundary samples redX[x] withx=0 . . . boundarySize−1 and upsampling boundary samples upsBdryX[x]with x=0 . . . upsBdrySize−1.

The upsampling boundary samples upsBdryX[x] with x=0 . . . upsBdrySize−1are derived as follows:

-   -   If needUpsBdryX is equal to TRUE and upsBdrySize is less than        nTbX, the following applies:

uDwn=nTbX/upsBdrySize   (8-X30)

upsBdryX[x]=(Σ_(i=0) ^(uDwn−1) refX[x*uDwn+i]+(1<<(Log 2(uDwn)−1)))>>Log2(uDwn)   (8-X31)

-   -   Otherwise (upsBdrySize is equal to nTbX), upsBdryX[x] is set        equal to refX[x].

The reduced boundary samples redX[x] with x=0 . . . boundarySize−1 arederived as follows:

-   -   If boundarySize is less than upsBdrySize, the following applies:

bDwn=upsBdrySize/boundarySize   (8-X32)

redX[x]=(Σ_(i=0) ^(bDwn−1) upsBdryX[x*bDwn+i]+(1<<(Log 2(bDwn)−1)))>>Log2(bDwn)   (8-X33)

-   -   Otherwise (boundarySize is equal to upsBdrySize), redX[x] is set        equal to upsBdryX[x].

8.4.4.2.X4 Specification of the Prediction Upsampling Process

Inputs to this process are:

-   -   a variable predW specifying the input block width,    -   a variable predH specifying the input block height,    -   affine linear weighted samples predLwip[x][y], with x=0 . . .        predW−1, y=0 . . . predH−1,    -   a variable nTbW specifying the transform block width,    -   a variable nTbH specifying the transform block height,    -   a variable upsBdryW specifying the upsampling boundary width,    -   a variable upsBdryH specifying the upsampling boundary height,    -   top upsampling boundary samples upsBdryT[x] with x=0 . . .        upsBdryW−1,    -   left upsampling boundary samples upsBdryL[x] with x=0 . . .        upsBdryH−1.

Outputs of this process are the predicted samples predSamples[x][y],with x=0 . . . nTbW−1, y=0 . . . nTbH−1.

The sparse predicted samples predSamples[m][n] are derived frompredLwip[x][y], with x=0 . . . predW−1, y=0 . . . predH−1 as follows:

upHor=nTbW/predW   (8-X34)

upVer=nTbH/predH   (8-X35)

predSamples[(x+1)*upHor−1][(y+1)*upVer−1]=predLwip[x][y]  (8-X36)

The top boundary samples upsBdryT[x] with x=0 . . . upsBdryW−1 areassigned to predSamples[m][−1] as follows:

predSamples[(x+1)*(nTbW/upsBdryW)−1][−1]=upsBdryT[x]  (8-X37)

The left boundary samples upsBdryL[y] with y=0 . . . upsBdryH−1 areassigned to predSamples[−1][n] as follows:

predSamples[−1][(y+1)*(nTbH/upsBdryH)−1]=upsBdryL[y]  (8-X38)

The predicted samples predSamples[x][y], with x=0 . . . nTbW−1, y=0 . .. nTbH−1 are derived as follows:

-   -   If nTbH is greater than nTbW, the following ordered steps apply:        -   1. When upHor is greater than 1, horizontal upsampling for            all sparse positions (xHor, yHor)=(m*upHor−1, n*upVer−1)            with m=0 . . . predW−1, n=1 . . . predH is applied with dX=1            . . . upHor−1 as follows:

predSamples[xHor+dX][yHor]=((upHor−dX)*predSamples[xHor][yHor]+dX*predSamples[xHor+upHor][yHor])/upHor  (8-X39)

-   -   -   2. Vertical upsampling for all sparse positions (xVer,            yVer)=(m, n*upVer−1) with m=0 . . . nTbW−1, n=0 . . .            predH−1 is applied with dY=1 . . . upVer−1 as follows:

predSamples[xVer][yVer+dY]=((upVer−dY)*predSamples[xVer][yVer]+dY*predSamples[xVer][yVer+upVer])/upVer  (8-X40)

-   -   Otherwise, the following ordered steps apply:        -   1. When upVer is greater than 1, vertical upsampling for all            sparse positions (xVer, yVer)=(m*upHor−1, n*upVer−1) with            m=1 . . . predW, n=0 . . . predH'1 is applied with dY=1 . .            . upVer−1 as specified in (8-X40).        -   2. Horizontal upsampling for all sparse positions (xHor,            yHor)=(m*upHor−1, n) with m=0 . . . predW−1, n=0 . . .            nTbH−1 is applied with dX=1 . . . upHor−1 as specified in            (8-X39).

<end>

TABLE 9-9 Syntax elements and associated binarizations BinarizationSyntax structure Syntax element Process Input parameters coding_unit( )cu_skip_flag[ ][ ] FL cMax = 1 pred_mode_ibc_flag FL cMax = 1pred_mode_flag FL cMax = 1 <begin>intra_lwip_flag[ ][ ] FL cMax = 1intra_lwip_mpm_flag[ ][ ] FL cMax = 1 intra_lwip_mpm_idx[ ][ ] TR cMax =2, cRiceParam = 0 intra_lwip_mpm_remainder[ ][ ] FL cMax = (cbWidth = =4 && cbHeight = = 4) ? 31 : ( (cbWidth <= 8 && cbHeight <=8) ? 15: 7) .. .

TABLE 9-15 Assignment of ctxInc to syntax elements with context codedbins binIdx Syntax element 0 I 2 3 4 >=5 . . . terminate na na na na naintra_lwip_flag[ ][ ] (Abs( Log2(cbWidth) − na na na na naLog2(cbHeight) ) > 1) ? 3: ( 0, 1, 2 (clause 9.5.4.2.2) )intra_lwip_mpm_flag[ ][ ] 0 na na na na na intra_lwip_mpm_idx[ ][ ]bypass bypass na na na na intra_lwip_mpm_remainder[ ][ ] bypass bypassbypass bypass bypass na

TABLE 9-16 Specification of ctxInc using left and above syntax elementsSyntax element condL condA ctxSetIdx . . . intra_lwip_flag[ x0 ][ y0 ]intra_lwip_flag[ xNbL ][ yNbL ] intra_lwip_flag[ xNbA ][ yNbA ] 0 . . .

<end>

Summary of ALWIP

For predicting the samples of a rectangular block of width W and heightH, affine linear weighted intra prediction (ALWIP) takes one line of Hreconstructed neighboring boundary samples left of the block and oneline of W reconstructed neighboring boundary samples above the block asinput. If the reconstructed samples are unavailable, they are generatedas it is done in the conventional intra prediction. ALWIP is onlyapplied to luma intra block. For chroma intra block, the conventionalintra coding modes are applied.

The generation of the prediction signal is based on the following threesteps:

-   -   1. Out of the boundary samples, four samples in the case of        W=H=4 and eight samples in all other cases are extracted by        averaging.    -   2. A matrix vector multiplication, followed by addition of an        offset, is carried out with the averaged samples as an input.        The result is a reduced prediction signal on a subsampled set of        samples in the original block.    -   3. The prediction signal at the remaining positions is generated        from the prediction signal on the subsampled set by linear        interpolation which is a single step linear interpolation in        each direction.

If an ALWIP mode is to be applied, the index predmode of the ALWIP modeis signaled using a MPM-list with 3 MPMS. Here, the derivation of theMPMs is performed using the intra-modes of the above and the left PU asfollows. There are three fixed tables map_angular_to_alwip_(idx), idx ∈{0, 1, 2} that assign to each conventional intra prediction modepredmode_(Angular) an ALWIP mode

predmode_(ALWIP)=map_angular_to_alwip_(idx)[predmode_(Angular)].

For each PU of width W and height H one defines an index

idx(PU)=idx(W, H) ∈ {0, 1, 2}

that indicates from which of the three sets the ALWIP-parameters are tobe taken.

If the above Prediction Unit PU_(above) is available, belongs to thesame CTU as the current PU and is in intra mode, ifidx(PU)=idx(PU_(above)) and if ALWIP is applied on PU_(above) withALWIP-mode predmode_(ALWIP) ^(above), one puts

mode_(ALWIP) ^(above)=predmode_(ALWIP) ^(above).

If the above PU is available, belongs to the same CTU as the current PUand is in intra mode and if a conventional intra prediction modepredmode_(Angular) ^(above) is applied on the above PU, one puts

mode_(ALWIP) ^(above)=map_angular_to_alwip_(idx(PU) _(above)₎[predmode_(Angular) ^(above)].

In all other cases, one puts

mode_(ALWIP) ^(above)=−1

which means that this mode is unavailable. In the same way but withoutthe restriction that the left PU needs to belong to the same CTU as thecurrent PU, one derives a mode mode_(ALWIP) ^(left).

Finally, three fixed default lists list_(idx), idx ∈ {0, 1, 2} areprovided, each of which contains three distinct ALWIP modes. Out of thedefault list list_(idx(PU)) and the modes mode_(ALWIP) ^(above) andmode_(ALWIP) ^(left), one constructs three distinct MPMs by substituting−1 by default values as well as eliminating repetitions.

For the luma MPM-list derivation, whenever a neighboring luma block isencountered which uses an ALWIP-mode predmode_(ALWIP), this block istreated as if it was using the conventional intra-prediction modepredmode_(Angular).

predmode_(Angular)=map_alwip_to_angular_(idx(PU))[predmode_(ALWIP)]

3 Transform in VVC 3.1 Multiple Transform Selection (MTS)

In addition to DCT-II which has been employed in HEVC, a MultipleTransform Selection (MTS) scheme is used for residual coding both interand intra coded blocks. It uses multiple selected transforms from theDCT8/DST7. The newly introduced transform matrices are DST-VII andDCT-VIII.

3.2 Reduced Secondary Transform (RST) Proposed in JVET-N0193

Reduced secondary transform (RST) applies 16×16 and 16×64 non-separabletransform for 4×4 and 8×8 blocks, respectively. Primary forward andinverse transforms are still performed the same way as two 1-Dhorizontal/vertical transform passes. Secondary forward and inversetransforms are a separate process step from that of primary transforms.For encoder, primary forward transform is performed first, then followedby secondary forward transform and quantization, and CABAC bit encoding.For decoder, CABAC bit decoding and inverse quantization, then Secondaryinverse transform is performed first, then followed by primary inversetransform. RST applies only to intra coded TUs in both intra slice andinter slices.

3.3 A Unified MPM List for Intra Mode Coding in JVET-N0185

A unified 6-MPM list is proposed for intra blocks irrespective ofwhether Multiple Reference Line (MRL) and Intra sub-partition (ISP)coding tools are applied or not. The MPM list is constructed based onintra modes of the left and above neighboring block as in VTM4.0.Suppose the mode of the left is denoted as Left and the mode of theabove block is denoted as Above, the unified MPM list is constructed asfollows:

-   -   When a neighboring block is not available, its intra mode is set        to Planar by default.    -   If both modes Left and Above are non-angular modes:    -   a. MPM list→{Planar, DC, V, H, V−4, V+4}    -   If one of modes Left and Above is angular mode, and the other is        non-angular:    -   a. Set a mode Max as the larger mode in Left and Above    -   b. MPM list→{Planar, Max, DC, Max −1, Max +1, Max −2}    -   If Left and Above are both angular and they are different:    -   a. Set a mode Max as the larger mode in Left and Above    -   b. if the difference of mode Left and Above is in the range of 2        to 62, inclusive        -   i. MPM list→{Planar, Left, Above, DC, Max −1, Max +1}    -   c. Otherwise        -   i. MPM list→{Planar, Left, Above, DC, Max −2, Max +2}    -   If Left and Above are both angular and they are the same:    -   a. MPM list→{Planar, Left, Left −1, Left +1, DC, Left −2}

Besides, the first bin of the MPM index codeword is CABAC context coded.In total three contexts are used, corresponding to whether the currentintra block is MRL enabled, ISP enabled, or a normal intra block.

The left neighboring block and above neighboring block used in theunified MPM list construction is A2 and B2 as shown in FIG. 10.

One MPM flag is firstly coded. If the block is coded with one of mode inthe MPM list, an MPM index is further coded. Otherwise, an index to theremaining modes (excluding MPMs) is coded.

4 Examples of Drawbacks in Existing Implementations

The design of ALWIP in JVET-N0217 has the following problems:

-   -   1) At the March 2019 JVET meeting, a unified 6-MPM list        generation was adopted for MRL mode, ISP mode, and normal intra        mode. But the affine linear weighted prediction mode uses a        different 3-MPM list construction which makes the MPM list        construction complicated. A complex MPM list construction might        compromise the throughput of the decoder, in particular for        small blocks such as 4×4 samples.    -   2) ALWIP is only applied to luma component of the block. For the        chroma component of an ALWP coded block, a chroma mode index is        coded and sent to decoder, which could result in unnecessary        signaling.    -   3) The interactions of ALWIP with other coding tools should be        considered.    -   4) When calculating upsBdryX in upsBdryX[x]=(Σ_(i=0) ^(uDwn−1)        refX[x*uDwn+i]+(1<<(Log 2(uDwn)−1)))>>Log 2(uDwn) (8-X31), it is        possible that Log 2(uDwn)−1 is equal to −1, while left shifted        with −1 is undefined.    -   5) When upsampling the prediction samples, no rounding is        applied.    -   6) In the deblocking process, ALWIP coded blocks are treated as        normal intra-blocks.

5 Exemplary Methods for Matrix-Based Intra Coding

Embodiments of the presently disclosed technology overcome drawbacks ofexisting implementations, thereby providing video coding with highercoding efficiencies but lower computational complexity. Matrix-basedintra prediction methods for video coding, and as described in thepresent document, may enhance both existing and future video codingstandards, is elucidated in the following examples described for variousimplementations. The examples of the disclosed technology provided belowexplain general concepts, and are not meant to be interpreted aslimiting. In an example, unless explicitly indicated to the contrary,the various features described in these examples may be combined.

In the following discussion, an intra-prediction mode refers to anangular intra prediction mode (including DC, planar, CCLM and otherpossible intra prediction modes); while an intra mode refers to normalintra mode, or MRL, or ISP or ALWIP.

In the following discussion, “Other intra modes” may refer to one ormultiple intra modes except ALWIP, such as normal intra mode, or MRL, orISP.

In the following discussion, SatShift(x, n) is defined as

${{SatShift}\left( {x,n} \right)} = \left\{ \begin{matrix}{{\left( {x + {{offset}\; 0}} \right) ⪢ n}\mspace{7mu}} & {if} & {x \geq 0} \\{- \left( {\left( {{- x} + {{offset}\; 1}} \right) ⪢ n} \right)} & {if} & {x < 0}\end{matrix} \right.$

Shift(x, n) is defined as Shift(x, n)=(x+offset0)>>n.

In one example, offset0 and/or offset1 are set to (1<<n)>>1 or(1<<(n−1)). In another example, offset0 and/or offset1 are set to 0.

In another example, offset0=offset1=((1<<n)>>1)−1 or ((1<<(n−1)))−1.

Clip3(min, max, x) is defined as

${{{Clip}3}\left( {{Min},{Max},x} \right)} = \left\{ \begin{matrix}{Min} & {if} & {x < {Min}} \\{Max} & {if} & {x > {Max}} \\x & {\;{otherwise}} & \;\end{matrix} \right.$

MPM List Construction for ALWIP

-   -   1. It is proposed that the whole or partial of the MPM list for        ALWIP may be constructed according to the whole or partial        procedure to construct the MPM list for non-ALWIP intra mode        (such as normal intra mode, MRL, or ISP).        -   a. In one example, the size of the MPM list for ALWIP may be            the same as that of the MPM list for non-ALWIP intra mode.            -   i. For example, the size of MPM list is 6 for both ALWIP                and non-ALWIP intra modes.        -   b. In one example, the MPM list for ALWIP may be derived            from the MPM list for non-ALWIP intra mode.            -   i. In one example, the MPM list for non-ALWIP intra mode                may be firstly constructed. Afterwards, partial or all                of them may be converted to the MPMs which may be                further added to the MPM list for ALWIP coded blocks.                -   1) Alternatively, furthermore, when adding a                    converted MPM to the MPM list for ALWIP coded                    blocks, pruning may be applied.                -   2) Default modes may be added to the MPM list for                    ALWIP coded blocks.                -    a. In one example, default modes may be added                    before those converted from the MPM list of                    non-ALWIP intra mode.                -    b. Alternatively, default modes may be added after                    those converted from the MPM list of non-ALWIP intra                    mode.                -    c. Alternatively, default modes may be added in an                    interleaved way with those converted from the MPM                    list of non-ALWIP intra mode.                -    d. In one example, the default modes may be fixed                    to be the same for all kinds of blocks.                -    e. Alternatively, the default modes may be                    determined according to coded information, such as                    availability of neighboring blocks, mode information                    of neighboring blocks, block dimension.            -   ii. In one example, one intra-prediction mode in the MPM                list for non-ALWIP intra mode may be converted to its                corresponding ALWIP intra-prediction mode, when it is                put into the MPM list for ALWIP.                -   1) Alternatively, all the intra-prediction modes in                    the MPM list for non-ALWIP intra modes may be                    converted to corresponding ALWIP intra-prediction                    modes before being used to construct the MPM list                    for ALWIP.                -   2) Alternatively, all the candidate intra-prediction                    modes (may include the intra-prediction modes from                    neighboring blocks and default intra-prediction                    modes such as Planar and DC) may be converted to                    corresponding ALWIP intra-prediction modes before                    being used to construct the MPM list for non-ALWIP                    intra modes, if the MPM list for non-ALWIP intra                    modes may be further used to derive the MPM list for                    ALWIP.                -   3) In one example, two converted ALWIP                    intra-prediction modes may be compared.                -    a. In one example, if they are the same, only one                    of them may be put into the MPM list for ALWIP.                -    b. In one example, if they are the same, only one                    of them may be put into the MPM list for non-ALWIP                    intra modes.            -   iii. In one example, K out of S intra-prediction modes                in the MPM list for non-ALWIP intra modes may be picked                as the MPM list for ALWIP mode. E.g., K is equal to 3                and S is equal to 6.                -   1) In one example, the first K intra-prediction                    modes in the MPM list for non-ALWIP intra modes may                    be picked as the MPM list for ALWIP mode.    -   2. It is proposed that the one or multiple neighboring blocks        used to derive the MPM list for ALWIP may also be used to used        derive the MPM list for non-ALWIP intra modes (such as normal        intra mode, MRL, or ISP).        -   a. In one example, the neighboring block left to the current            block used to derive the MPM list for ALWIP should be the            same as that used to derive the MPM list for non-ALWIP intra            modes.            -   i. Suppose the top-left corner of the current block is                (xCb, yCb), the width and height of the current block                are W and H, then in one example, the left neighboring                block used to derive the MPM list for both ALWIP and                non-ALWIP intra modes may cover the position (xCb−1,                yCb). In an alternative example, the left neighboring                block used to derive the MPM list for both ALWIP and                non-ALWIP intra modes may cover the position (xCb−1,                yCb+H−1).            -   ii. For example, the left neighboring block and above                neighboring block used in the unified MPM list                construction is A2 and B2 as shown in FIG. 10.        -   b. In one example, the neighboring block above to the            current block used to derive the MPM list for ALWIP should            be the same as that used to derive the MPM list for            non-ALWIP intra modes.            -   i. Suppose the top-left corner of the current block is                (xCb, yCb), the width and height of the current block                are W and H, then in one example, the above neighboring                block used to derive the MPM list for both ALWIP and                non-ALWIP intra modes may cover the position (xCb,                yCb−1). In an alternative example, the above neighboring                block used to derive the MPM list for both ALWIP and                non-ALWIP intra modes may cover the position (xCb+W−1,                yCb−1).            -   ii. For example, the left neighboring block and above                neighboring block used in the unified MPM list                construction is A1 and B1 as shown in FIG. 10.    -   3. It is proposed that the MPM list for ALWIP may be constructed        in different ways according to the width and/or height of the        current block.        -   a. In one example, different neighboring blocks may be            accessed for different block dimensions.    -   4. It is proposed that the MPM list for ALWIP and the MPM list        for non-ALWIP intra modes may be constructed with the same        procedure but with different parameters.        -   a. In one example, K out of S intra-prediction modes in the            MPM list construction procedure of non-ALWIP intra modes may            be derived for the MPM list used in ALWIP mode. E.g., K is            equal to 3 and S is equal to 6.            -   i. In one example, the first K intra-prediction modes in                the MPM list construction procedure may be derived for                the MPM list used in ALWIP mode.        -   b. In one example, the first mode in the MPM list may be            different.            -   i. For example, the first mode in the MPM list for                non-ALWIP intra modes may be Planar, but it may be a                Mode X0 in the MPM list for ALWIP.                -   1) In one example, X0 may be the ALWIP                    intra-prediction mode converted from Planar.        -   c. In one example, stuffing modes in the MPM list may be            different.            -   i. For example, the first three stuffing modes in the                MPM list for non-ALWIP intra modes may be DC, Vertical                and Horizontal, but they may be Mode X1, X2, X3 in the                MPM list for ALWIP.                -   1) In one example, X1, X2, X3 may be different for                    different sizeId.            -   ii. In one example, the number of stuffing mode may be                different.        -   d. In one example, neighboring modes in the MPM list may be            different.            -   i. For example, the normal intra-prediction modes of                neighboring blocks are used to construct the MPM list                for non-ALWIP intra modes. And they are converted to                ALWIP intra-prediction modes to construct the MPM list                for ALWIP mode.        -   e. In one example, the shifted modes in the MPM list may be            different.            -   i. For example, X+K0 where X is a normal                intra-prediction mode and K0 is an integer may be put                into the MPM list for non-ALWIP intra modes. And Y+K1                where Y is an ALWIP intra-prediction mode and K1 is an                integer may be put into the MPM list for ALWIP, where K0                may be different from K1.                -   1) In one example, K1 may depend on the width and                    height.    -   5. It is proposed that a neighboring block is treated as        unavailable if it is coded with ALWIP when constructing the MPM        list for the current block with non-ALWIP intra modes.        -   a. Alternatively, a neighboring block is treated as being            coded with a predefined intra-prediction mode (such as            Planar) if it is coded with ALWIP when constructing the MPM            list for the current block with non-ALWIP intra modes.    -   6. It is proposed that a neighboring block is treated as        unavailable if it is coded with non-ALWIP intra modes when        constructing the MPM list for the current block with ALWIP mode.        -   a. Alternatively, a neighboring block is treated as being            coded with a predefined ALWIP intra-prediction mode X if it            is coded with non-ALWIP intra modes when constructing the            MPM list for the current block with ALWIP mode.            -   i. In one example, X may depend on the block dimensions,                such as width and/or height.    -   7. It is proposed to remove the storage of ALWIP flag from line        buffer.        -   a. In one example, when the 2^(nd) block to be accessed is            located in a different LCU/CTU row/region compared to the            current block, the conditional check of whether the 2^(nd)            block is coded with ALWIP is skipped.        -   b. In one example, when the 2^(nd) block to be accessed is            located in a different LCU/CTU row/region compared to the            current block, the 2^(nd) block is treated in the same way            as non-ALWIP mode, such as treated as normal intra coded            block.    -   8. When encoding the ALWIP flag, no more than K (K>=0) contexts        may be used.        -   a. In one example, K=1.    -   9. It is proposed to store the converted intra prediction mode        of ALWIP coded blocks instead of directly storing the mode index        associated with the ALWIP mode.        -   a. In one example, the decoded mode index associated with            one ALWIP coded block is mapped to the normal intra mode,            such as according to map_alwip_to_angular as described in            Section 2.5.7.        -   b. Alternatively, furthermore, the storage of ALWIP flag is            totally removed.        -   c. Alternatively, furthermore, the storage of ALWIP mode is            totally removed.        -   d. Alternatively, furthermore, condition check of whether            one neighboring/current block is coded with ALWIP flag may            be skipped.        -   e. Alternatively, furthermore, the conversion of modes            assigned for ALWIP coded blocks and normal intra predictions            associated with one accessed block may be skipped.

ALWIP on Different Color Components

-   -   10. It is proposed that an inferred chroma intra mode (e.g., DM        mode) might be always applied if the corresponding luma block is        coded with ALWIP mode.        -   a. In one example, chroma intra mode is inferred to be DM            mode without signaling if the corresponding luma block is            coded with ALWIP mode.        -   b. In one example, the corresponding luma block may be the            one covering the corresponding sample of a chroma sample            located at a given position (e.g., top-left of current            chroma block, center of current chroma block).        -   c. In one example, the DM mode may be derived according to            the intra prediction mode of the corresponding luma block,            such as via mapping the (ALWIP) mode to one of the normal            intra mode.    -   11. When the corresponding luma block of the chroma blocks is        coded with ALWIP mode, several DM modes may be derived.    -   12. It is proposed that a special mode is assigned to the chroma        blocks if one corresponding luma block is coded with ALWIP mode.        -   a. In one example, the special mode is defined to be a given            normal intra prediction mode regardless the intra prediction            mode associated with the ALWIP coded blocks.        -   b. In one example, different ways of intra prediction may be            assigned to this special mode.    -   13. It is proposed that ALWIP may also be applied to chroma        components.        -   a. In one example, the matrix and/or bias vector may be            different for different color components.        -   b. In one example, the matrix and/or bias vector may be            predefined jointly for Cb and Cr.            -   i. In one example, Cb and Cr component may be                concatenated.            -   ii. In one example, Cb and Cr component may be                interleaved.        -   c. In one example, the chroma component may share the same            ALWIP intra-prediction mode as the corresponding luma block.            -   i. In one example, the same ALWIP intra-prediction mode                is applied on the chroma component if the corresponding                luma block applies the ALWIP mode and the chroma block                is coded with DM mode.            -   ii. In one example, the same ALWIP intra-prediction mode                is applied on the chroma component and the linear                interpolation thereafter can be skipped.            -   iii. In one example, the same ALWIP intra-prediction                mode is applied on the chroma component with a                subsampled matrix and/or bias vector.        -   d. In one example, the number of ALWIP intra-prediction            modes for different component may be different.            -   i. For example, the number of ALWIP intra-prediction                modes for chroma components may be less than that for                luma component for the same block width and height.

Applicability of ALWIP

-   -   14. It is proposed that whether ALWIP can be applied may be        signaled.        -   a. For example, it may be signaled at sequence level (e.g.            in SPS), at picture level (e.g. in PPS or picture header),            at slice level (e.g. in slice header), at tile group level            (e.g. in tile group header), at tile level, at CTU row            level, or at CTU level.        -   b. For example, intra_lwip_flag may not be signaled and            inferred to be 0 if ALWIP cannot be applied.    -   15. It is proposed that whether ALWIP can be applied may depend        on the block width (W) and/or height (H).        -   c. For example, ALWIP may not be applied if W>=T1 (or W>T1)            and H>=T2 (or H>T2). E.g. T1=T2=32;            -   i. For example, ALWIP may not be applied if W<=T1 (or                W<T1) and H<=T2 (or H<T2). E.g. T1=T2=32;        -   d. For example, ALWIP may not be applied if W>=T1 (or W>T1)            or H>=T2 (or H>T2). E.g. T1=T2=32;            -   i. For example, ALWIP may not be applied if W<=T1 (or                W<T1) or H<=T2 (or H<T2). E.g. T1=T2=32;        -   e. For example, ALWIP may not be applied if W+H>=T (or            W*H>T). E.g. T=256;            -   i. For example, ALWIP may not be applied if W+H<=T (or                W+H<T). E.g. T=256;        -   f. For example, ALWIP may not be applied if W*H>=T (or            W*H>T). E.g. T=256;            -   i. For example, ALWIP may not be applied if W*H<=T (or                W*H<T). E.g. T=256;        -   g. For example, intra_lwip_flag may not be signaled and            inferred to be 0 if ALWIP cannot be applied.

Calculation Problems in ALWIP

-   -   16. It is proposed that any shift operation involved in ALWIP        can only left shift or right shift a number by S, where S must        be larger or equal to 0.        -   a. In one example, the right shift operation may be            different when S is equal to 0 or larger than 0.            -   i. In one example, upsBdryX[x] should be calculated as

upsBdryX[x]=(Σ_(i=0) ^(uDwn−1) refX[x*uDwn+i]+(1<<(Log 2(uDwn)−1)))>>Log2(uDwn) when uDwn>1, and

upsBdryX[x]=Σ_(i=0) ^(uDwn−1) refX[x*uDwn+i] when uDwn is equal to 1.

-   -   -   b. In one example, upsBdryX[x] should be calculated as

upsBdryX[x]=(Σ_(i=0) ^(uDwn−1) refX[x*uDwn+i]+(1<<Log 2(uDwn)>>1))>>Log2(uDwn)

-   -   17. It is proposed that the results should be rounded        toward-zero or away-from-zero in the up-sampling process of        ALWIP.        -   a. In one example,

predSamples[xHor+dX][yHor]=((upHor−dX)*predSamples[xHor][yHor]+dX*predSamples[xHor+upHor][yHor]+offsetHor)/upHor  (8-X39)

and

predSamples[xVer][yVer+dY]=((upVer−dY)*predSamples[xVer][yVer]+dY*predSamples[xVer][yVer+upVer]+offsetVer)/upVer  (8-X40)

-   -    where offsetHor and offsetVer are integers. For example,        offsetHor=upHor/2 and offsetVer=upVer/2.        Interaction with Other Coding Tools    -   18. It is proposed that ALWIP may be used for a CIIP-coded        block.        -   a. In one example, in a CIIP-coded block, it may be            explicitly signaled whether an ALWIP intra-prediction mode            or a normal intra prediction mode such as Planar is used to            generate the intra prediction signal.        -   b. In one example, it may be implicitly inferred whether an            ALWIP intra-prediction mode or a normal intra prediction            mode such as Planar may be used to generate the intra            prediction signal.            -   i. In one example, ALWIP intra-prediction mode may never                be used in a CIIP coded block.                -   1) Alternatively, normal intra prediction may never                    be used in a CIIP coded block.            -   ii. In one example, it may be inferred from information                of neighboring blocks whether an ALWIP intra-prediction                mode or a normal intra prediction mode such as Planar is                used to generate the intra prediction signal.    -   19. It is proposed that the whole or partial of the procedure        used to down-sample the neighboring luma samples in the CCLM        mode may be used to down-sample the neighboring samples in the        ALWIP mode.        -   a. Alternatively, the whole or partial of the procedure used            to down-sample the neighboring luma samples in the ALWIP            mode may be used to down-sample the neighboring samples in            the CCLM mode.        -   b. The down-sampling procedure may be invoked with different            parameters/arguments when it is used in the CCLM process and            ALWIP process.        -   c. In one example, the down-sampling method (such as            selection of neighboring luma locations, down-sampling            filters) in the CCLM process may be utilized in the ALWIP            process.        -   d. The procedure used to down-sample the neighboring luma            samples at least include the selection of down-sampled            positions, the down-sampling filters, the rounding and            clipping operations.    -   20. It is proposed that a block coded with ALWIP mode cannot        apply RST or/and secondary transform or/and rotation transform        or/and Non-Separable Secondary Transform (NSST).        -   a. In one example, whether such constraint may be applied or            not may depend on the dimension information of the block,            e.g., same as conditions described in (15).        -   b. Alternatively, ALWIP mode may be disallowed when RST            or/and secondary transform or/and rotation transform or/and            NSST is applied.        -   c. Alternatively, a block coded with ALWIP mode may apply            RST or/and secondary transform or/and rotation transform            or/and Non-Separable Secondary Transform (NSST).            -   i. In one example, the selection of transform matrix may                depend the ALWIP intra-prediction mode.            -   ii. In one example, the selection of transform matrix                may depend the normal intra-prediction mode which is                converted from the ALWIP intra-prediction mode.            -   iii. In one example, the selection of transform matrix                may depend the classification on the normal                intra-prediction mode which is converted from the ALWIP                intra-prediction mode.    -   21. It is proposed that a block coded with ALWIP mode cannot        apply Block-based DPCM (BDPCM) or Residue RDPCM.        -   a. Alternatively, ALWIP mode may be disallowed when BDPCM or            RDPCM is applied.    -   22. It is proposed that a block coded with ALWIP mode may only        use DCT-II as the transform.        -   a. In one example, the signalling of transform matrix            indices is always skipped.        -   b. Alternatively, it is proposed that the transform used for            a block coded with ALWIP mode may be implicitly derived            instead of explicitly signaled. For example, the transform            may be selected following the way proposed in JVET-M0303.        -   c. Alternatively, it is proposed that a block coded with            ALWIP mode may only use transform skip.            -   i. Alternatively, furthermore, when ALWIP is used, the                signalling of indication of usage of transform skip is                skipped.        -   d. In one example, ALWIP mode information (such as            enabled/disabled, prediction mode index) may be            conditionally signalled after indications of transform            matrix.            -   i. In one example, for a given transform matrix (such as                transform skip or DCT-II), the indications of ALWIP mode                information may be signalled.            -   ii. Alternatively, furthermore, the indications of ALWIP                mode information may be skipped for some pre-defined                transform matrices.    -   23. It is proposed that a block coded with ALWIP mode is        regarded to be coded with a normal intra-prediction converted        from the ALWIP intra-prediction mode when the selected transform        is mode-dependent.    -   24. ALWIP mode may not use transform skip.        -   a. For example, there is no need to further signal the            indication of usage of transform skip in this case.        -   b. Alternatively, ALWIP mode may be disallowed when            transform skip is applied.            -   i. For example, there is no need to signal ALWIP mode                information when transform skip is applied in this case.    -   25. In the filtering process, such as deblocking filter, sample        adaptive offset (SAO), adaptive loop filter (ALF), how to select        the filters and/or whether to filter samples may be determined        by the usage of ALWIP.    -   26. Unfiltered neighboring samples may be used in ALWIP mode.        -   a. Alternatively, filtered neighboring samples may be used            in ALWIP mode.        -   b. In one example, filtered neighboring samples may be used            for down sampling and unfiltered neighboring samples may be            used for up sampling.        -   c. In one example, unfiltered neighboring samples may be            used for down sampling and filtered neighboring samples may            be used for up sampling.        -   d. In one example, filtered left neighboring samples may be            used in up sampling and unfiltered above neighboring samples            may be used in up sampling.        -   e. In one example, unfiltered left neighboring samples may            be used in up sampling and filtered above neighboring            samples may be used in up sampling.        -   f. In one example, whether filter or unfiltered neighboring            samples is used may depend on the ALWIP mode.            -   i. In one example, ALWIP mode may be converted to                traditional intra prediction mode, and whether filtered                or unfiltered neighboring samples is used may depend on                the converted traditional intra prediction mode. For                example, such decision is same as traditional intra                prediction modes.            -   ii. Alternatively, whether filter or unfiltered                neighboring samples is used for ALWIP mode may be                signaled.        -   g. In one example, the filtered samples may be generated            same as traditional intra prediction modes.    -   27. Which matrices or/and offset vectors are used may depend on        reshaping (a.k.a. LMCS, luma mapping with chroma scaling)        information.        -   a. In one example, different matrices or/and offset vectors            may be used when reshaping is on and off.        -   b. In one example, different matrices or/and offset vectors            may be used for different reshaping parameters.        -   c. In one example, ALWIP may be always performed in original            domain.            -   i. For example, neighboring sample are mapped to the                original domain (if reshaping is applied) before used in                ALWIP.    -   28. ALWIP may be disabled when reshaping is applied.        -   a. Alternatively, reshaping may be disabled when ALWIP is            enabled.        -   b. In one example, ALWIP may be disabled for HDR (high            dynamic range) content when reshaping is applied.    -   29. The matrices used in ALWIP may depend on sample bit-depth.        -   a. Alternatively, furthermore, the offset values used in            ALWIP may depend on sample bit-depth.        -   b. Alternatively, the matrix parameters and offset values            can be stored in M-bit precision for N-bit samples (M<=N),            e.g., the matrix parameters and offset values can be stored            in 8-bit precision for a 10-bit sample.        -   c. The sample bit-depth may be the bit-depth of input array            for a color component such as luma.        -   d. The sample bit-depth may be the bit-depth of internal            array/reconstructed sample for a color component, such as            luma.    -   30. The matrix parameters and/or offset values for a specified        block size may be derived from the matrix parameters and/or        offset values for other block sizes.    -   31. In one example, the 16×8 matrix of 8×8 block can be derived        from the 16×4 matrix of 4×4 block.    -   32. It is proposed that the prediction generated by ALWIP may be        treated as an intermedium or intermediate signal which will be        processed to obtain the prediction signal to be further used.        -   a. In one example, Position Dependent Intra Prediction            Combination (PDPC) may be applied on the prediction            generated by ALWIP to generate the prediction signal to be            further used.            -   i. In one example, PDPC is done on an ALWIP coded block                in the same way as the block is coded with a specific                normal intra-prediction mode, such as Planar or DC.            -   ii. In one example, PDPC is done on an ALWIP coded block                in the same way as the block coded with a normal                intra-prediction mode which is converted from the ALWIP                intra-prediction mode.            -   iii. In one example, PDPC is applied on an ALWIP coded                block conditionally.                -   1) For example, PDPC is applied on an ALWIP coded                    block only when PDPC is applied on the normal                    intra-prediction mode which is converted from the                    ALWIP intra-prediction mode.        -   b. In one example, the boundary samples prediction generated            by ALWIP may be filtered with neighbouring samples to            generate the prediction signal to be further used.            -   i. In one example, filtering on boundary samples is done                on an ALWIP coded block in the same way as the block is                coded with a specific normal intra-prediction mode, such                as Planar or DC.            -   ii. In one example, filtering on boundary samples is                done on an ALWIP coded block in the same way as the                block coded with a normal intra-prediction mode which is                converted from the ALWIP intra-prediction mode.            -   iii. In one example, filtering on boundary samples is                applied on an ALWIP coded block conditionally.                -   1) For example, filtering on boundary samples is                    applied on an ALWIP coded block only when filtering                    on boundary samples is applied on the normal                    intra-prediction mode which is converted from the                    ALWIP intra-prediction mode.    -   33. It is proposed that interpolation filters other than        bilinear interpolation filter may be used in the up-sampling        process of ALWIP.        -   a. In one example, 4-tap interpolation filters may be used            in the up-sampling process of ALWIP.            -   i. For example, the 4-tap interpolation filters in VVC                used to do the motion compensation for chroma components                may be used in the up-sampling process of ALWIP.            -   ii. For example, the 4-tap interpolation filters in VVC                used to do angular intra-prediction may be used in the                up-sampling process of ALWIP.            -   iii. For example, the 8-tap interpolation filters in VVC                used to do the motion compensation for luma component                may be used in the up-sampling process of ALWIP.    -   34. Samples within a block coded in ALWIP mode may be predicted        in different ways.        -   a. In one example, for a W*H block, prediction of a sW*sH            sub-block within it may be generated by applying sW*sH ALWIP            to it.            -   i. In one example, for a W*H block, prediction of its                top-left W/2*H/2 block may be generated by applying                W/2*H/2 ALWIP to it.            -   ii. In one example, for a W*H block, prediction of its                left W/2*H block may be generated by applying W/2*H                ALWIP to it.            -   iii. In one example, for a W*H block, prediction of its                top W*H/2 block may be generated by applying W*H/2 ALWIP                to it.            -   iv. In one example, the sW*sH sub-block may have                available left or/and above neighboring samples.        -   b. In one example, how to decide the position of the            sub-block may depend on dimension of the block.            -   i. For example, when W>=H, prediction of its left W/2*H                block may be generated by applying W/2*H ALWIP to it.            -   ii. For example, when H>=W, prediction of its top W*H/2                block may be generated by applying W*H/2 ALWIP to it.            -   iii. For example, when W is equal to H, prediction of                its top-left W/2*H/2 block may be generated by applying                W/2*H/2 ALWIP to it.        -   c. In one example, furthermore, prediction of the remaining            samples (e.g., samples do not belong to the sW*sH sub-block)            may be generated by applying the W*H ALWIP.            -   i. Alternatively, prediction of the remaining samples                may be generated by applying conventional intra                prediction (e.g., using the converted intra prediction                mode as the intra mode).            -   ii. Furthermore, calculation may be skipped for samples                in the sW*sH sub-block.    -   35. Samples within a block coded in ALWIP mode may be predicted        in sub-block (e.g., with size sW*sH) level.        -   a. In one example, sW*sH ALWIP may be applied to each            sub-block using neighboring reconstructed samples (e.g., for            boundary sub-blocks) or/and neighboring predicted samples            (e.g., for inner sub-blocks).        -   b. In one example, sub-blocks may be predicted in            raster-scan order.        -   c. In one example, sub-blocks may be predicted in zigzag            order.        -   d. In one example, width (height) of sub-blocks may be no            larger than sWMax (sHMax).        -   e. In one example, when a block with either width or height            or both width and height are both larger than (or equal to)            a threshold L, the block may be split into multiple            sub-blocks.        -   f. The threshold L may be pre-defined or signaled in            SPS/PPS/picture/slice/tile group/tile level.            -   i. Alternatively, the thresholds may depend on certain                coded information, such as block size, picture type,                temporal layer index, etc. al.    -   36. It is proposed that the neighbouring samples (adjacent or        non-adjacent) are filtered before being used in ALWIP.        -   a. Alternatively, neighbouring samples are not filtered            before being used in ALWIP.        -   b. Alternatively, neighbouring samples are conditionally            filtered before being used in ALWIP.            -   i. For example, neighbouring samples are filtered before                being used in ALWIP only when the ALWIP intra-prediction                mode is equal to one or some specific values.    -   37. It is proposed that when coding the ALWIP flag, the method        to derive the context for the ALWIP flag in arithmetic coding is        the same for all dimensions of the current block.        -   a. In one example, the method to derive the context for the            ALWIP flag in arithmetic coding is the same when (Abs(Log            2(cbWidth)−Log 2(cbHeight)) is larger than 1 or not, where            CbWidth and CbHeight are the width and height of the current            block, respectively.        -   b. In one example, the derivation of the context for the            ALWIP flag in arithmetic coding only depends on neighboring            blocks' ALWIP information and/or the availability of the            neighbouring blocks.            -   i. In one example, multiple neighboring blocks ALWIP                information (e.g., intra_lwip_flag) and/or the                availability of the neighbouring blocks are directly                used. For example, the left and above neighbouring                blocks' ALWIP flags and/or the availability of the left                and neighbouring blocks are used to derive the context                for the ALWIP flag in arithmetic coding. An example is                shown in Table 2. Alternatively, furthermore, the                context index offset ctxInc=(condL && availableL)+(condA                && availableA)+ctxSetIdx*3.

TABLE 2 Specification of ctxInc using left and above syntax elementsSyntax element condL condA ctxSetIdx intra_lwip_flag[ intra_lwip_flag[intra_lwip_flag[ 0 x0 ][ y0 ] xNbL ][ yNbL ] xNbA ][ yNbA ]

-   -   -   -   ii. In one example, one of the neighboring block's ALWIP                information (e.g., intra_lwip_flag) is used to derive                the context for the ALWIP flag in arithmetic coding, and                the neighbouring block may be the left neighbouring                block. An example is shown in Table 3. Alternatively,                furthermore, the context index offset ctxInc=(condL &&                availableL)+ctxSetIdx*3.

TABLE 3 Specification of ctxInc using left and above syntax elementsSyntax element condL condA ctxSetIdx intra_lwip_flag[ intra_lwip_flag[xNbL ][ 0 x0 ][ y0 ] yNbL ]

-   -   -   -   iii. In one example, one of the neighboring block's                ALWIP flag information (e.g., intra_lwip_flag) is used                to derive the context for the ALWIP flag in arithmetic                coding, and the neighbouring block may be the above                neighbouring block. An example is shown in Table 4.                Alternatively, furthermore, the context index offset                ctxInc=(condA && availableA)+ctxSetIdx*3.

TABLE 4 Specification of ctxInc using left and above syntax elementsSyntax element condL condA ctxSetIdx intra_lwip_flag[ intra_lwip_flag[ 0x0 ][ y0 ] xNbA ][ yNbA ]

-   -   -   c. In one example, one fixed context is used for coding the            ALWIP flag in arithmetic coding.        -   d. In one example, ALWIP flag is bypass coded in arithmetic            coding.        -   e. Alternatively, K contexts may be used for coding ALWIP            flag in arithmetic coding. The context to be used may depend            on dimension (e.g. width denoted as W and height denoted            as H) of the block.            -   i. In one example, K is equal to 2. When W>N*H or H>N*W                (e.g., N=2), the first context is used, otherwise, the                second context is used.

    -   38. It is proposed that N (N>=0) contexts may be used to code        the ALWIP flag (e.g., intra_lwip_flag) in arithmetic coding.        -   a. In one example, N is equal to three. ALWIP flag and/or            availability of two neighboring or/and non-adjacent blocks            may be used for deriving the used context for the ALWIP flag            in arithmetic coding.            -   i. In one example, the two neighboring blocks may                include the above (e.g., B1 in FIG. 10) block and the                left (e.g., A1 in FIG. 10) block.            -   ii. In one example, the two neighboring blocks may                include the above block and the below-left (e.g., A2 in                FIG. 10) block.            -   iii. In one example, the two neighboring blocks may                include the above block and the above-right (e.g., B2 in                FIG. 10) block.            -   iv. In one example, the two neighboring blocks may                include the above-right (e.g., B2 in FIG. 10) block and                the left (e.g., A1 in FIG. 10) block.            -   v. In one example, the two neighboring blocks may                include the above-right (e.g., B2 in FIG. 10) block and                the below-left (e.g., A2 in FIG. 10) block.            -   vi. In one example, the two neighboring blocks may                include the left block (e.g., A1 in FIG. 10) and the                below-left (e.g., A2 in FIG. 10) block.            -   vii. In one example, the neighboring block may be                defined differently from FIG. 10. an example is                described in FIG. 16. The two neighboring blocks may                include any two of the {above-right, above, above-left,                left, below-left} blocks. E.g., The two neighboring                blocks may include any two of the blocks in {B0, B1, B2,                A0, A1}.        -   b. In one example, N is equal to two. ALWIP flag and/or            availability of one neighboring or/and non-adjacent block            may be used for deriving the used context for the ALWIP flag            in arithmetic coding.            -   i. In one example, the neighboring block may be anyone                of the {above-right, above, above-left, left,                below-left}. An example of the neighboring block is                described in FIG. 10.            -   ii. In one example, the neighboring block may be anyone                of the {above-right, above, above-left, left,                below-left} block. An example of the neighboring block                is described in FIG. 16.        -   c. In one example, one fixed context may be used for coding            ALWIP flag in arithmetic coding.        -   d. In one example, ALWIP flag may be bypass coded in            arithmetic coding. FIG. 16 shows an example of neighboring            blocks.

    -   39. It is proposed that the reduced boundary samples may be        generated without calculating the up-sampling boundary samples.        -   a. In one example, the reference samples located at the            upsampling boundary sample positions are directly used for            the prediction upsampling process.            -   i. In one example, the upsampling boundary samples may                not be computed by averaging multiple adjacent reference                samples.        -   b. In one example, the reduced boundary samples may be            directly calculated from reference samples and the            downscaling factor.            -   i. In one example, the downscaling factor may be                computed by the transform block size and the downsampled                boundary size.

    -   40. In one example, the samples may be with different precisions        in different filtering stages in the up-sampling process in        ALWIP. “Samples” may refer to prediction samples or any        intermedium samples before or after the up-sampling process.        -   a. In one example, samples are up-sampled along a first            dimension horizontally in a first filtering stage; then            samples are up-sampled along a second dimension vertically            in a second filtering stage in the up-sampling process in            ALWIP.            -   i. Alternatively, samples are up-sampled along a first                dimension vertically in a first filtering stage; then                samples are up-sampled along a second dimension                horizontally in a second filtering stage in the                up-sampling process in ALWIP.        -   b. In one example, the output up-sampling results without            right-shifting or division in the first filtering stage may            be used as the input samples to the second filtering stage.            -   i. In one example, the output up-sampling filtering                results in the second filtering stage may be                right-shifted by Shift1 or divided by Dem1 to derive the                final up-sampled results.            -   ii. In one example, the output up-sampling filtering                results in the first filtering stage may be                right-shifted by Shift2 or divided by Dem2 to derive the                final up-sampled results.                -   1) In one example, Shift1=2×Shift2; Dem1=Dem2×Dem2.            -   iii. In one example, the samples, which are input to the                second filtering stage but are not the output                up-sampling results in the first filtering stage, may be                left-shifted Shift3 or multiplied by Dem3 before being                input to the second filtering stage.                -   1) In one example, Shift3=Shift1; Dem3=Dem2.        -   c. In one example, the output up-sampling results in the            first filtering stage may be right-shifted by Shift1 or            divided by Dem1 before being used as the input samples to            the second filtering stage.            -   i. In one example, the output up-sampling filtering                results in the second filtering stage may be                right-shifted by Shift2 or divided by Dem2 to derive the                final up-sampled results, where Shift2 may be not equal                to Shift1, e.g. Shift2>Shift1; Dem2 may be not equal to                Dem1, e.g. Dem2>Dem1.            -   ii. In one example, the output up-sampling filtering                results in the first filtering stage may be                right-shifted by Shift3 or divided by Dem3 to derive the                final up-sampled results, where Shift3 may be equal to                Shift1; Dem3 maybe not equal to Dem1.                -   1) In one example, Shift3=Shift1+Shift2.            -   iii. In one example, the samples, which are input to the                second filtering stage but are not the output                up-sampling results in the first filtering stage, may be                left-shifted or multiplied by a factor before being                input to the second filtering stage.        -   d. In one example, the output up-sampling results in the            first filtering stage may be left-shifted by Shift1 or            multiplied by Dem1 before being used as the input samples to            the second filtering stage.            -   i. In one example, the output up-sampling filtering                results in the second filtering stage may be                right-shifted or divided by a factor to derive the final                up-sampled results.            -   ii. In one example, the output up-sampling filtering                results in the first filtering stage may be                right-shifted or divided by a factor to derive the final                up-sampled results.            -   iii. In one example, the samples, which are input to the                second filtering stage but are not the output                up-sampling results in the first filtering stage, may be                left-shifted by Shift2 or multiplied by Dem2 before                being input to the second filtering stage, where Shift2                may be not equal to Shift1, e.g. Shift2>Shift1; Dem1 may                be not equal to Dem2, e.g. Dem2>Dem1.        -   e. In one example, the samples which are input to the first            filtering stage may be left-shifted by Shift1 or multiplied            by Dem1 before being used as the input samples to the first            filtering stage.            -   i. In one example, the output up-sampling filtering                results in the second filtering stage may be                right-shifted or divided by a factor to derive the final                up-sampled results.            -   ii. In one example, the output up-sampling filtering                results in the first filtering stage may be                right-shifted or divided by a factor to derive the final                up-sampled results.            -   iii. In one example, the samples, which are input to the                second filtering stage but are not the output                up-sampling results in the first filtering stage, may be                left-shifted by Shift2 or multiplied by Dem2 before                being input to the second filtering stage, where Shift2                may be not equal to Shift1, e.g. Shift2>Shift1; Dem2 may                be not equal to Dem1, e.g. Dem2>Dem1.

5. Embodiments

Newly added parts are highlighted in bold faced italics and deletedparts are highlighted in underlined italicized text.

5.1 One Example

Three contexts are used for coding ALWIP flag.

TABLE 9-15 Assignment of ctxInc to syntax elements with context codedbins

. . . terminate na na na na na intra_lwip_flag[ ][ ](Abs( Log2(cbWidth) − na na na na na Log2(cbHeight) ) > 1) ?3: ( 0, 1, 2 (clause 9.5.4.2.2) ) intra_lwip_flag[ ][ ] ( 0, 1, 2 na nana na na (clause 9.5.4.2.2) ) intra_lwip_mpm_flag[ ][ ] 0 na na na na naintra_lwip_mpm_idx[ ][ ] bypass bypass na na na na

TABLE 9-15 Assignment of ctxInc to syntax elements with context codedbins

intra_lwip_mpm_ bypass bypass bypass bypass bypass na remainder[ ][ ]

5.2 One Example

One fixed context is used for coding ALWIP flag.

TABLE 9-15 Assignment of ctxInc to syntax elements with context codedbins

. . . terminate na na na na na intra_lwip_flag[ ][ ](Abs( Log2(cbWidth) − na na na na na Log2(cbHeight) ) > 1) ?3: ( 0, 1, 2 (clause 9.5.4.2.2) )

intra_lwip_mpm_flag[ ][ ] 0 na na na na na intra_lwip_mpm_idx[ ][ ]bypass bypass na na na na intra_lwip_mpm_remainder[ ][ ] bypass bypassbypass bypass bypass na

5.3 One Example

Perform the boundary reduction process in one-step.

Below embodiments are based on the adoptedJVET-N0220-proposal-test-CE3-4.1_v2.

8.4.4.2.X1 Affine Linear Weighted Intra Sample Prediction 8.4.4.2.X3Specification of the Boundary Reduction Process

Inputs to this process are:

-   -   a variable nTbX specifying the transform block size,    -   reference samples refX[x] with x=0 . . . nTbX−1,    -   a variable boundarySize specifying the downsampled boundary        size,    -   a flag needUpsBdryX specifying whether intermediate boundary        samples are required for upsampling,    -   a variable upsBdrySize specifying the boundary size for        upsampling.

Outputs of this process are the reduced boundary samples redX[x] withx=0 . . . boundarySize−1 and upsampling boundary samples upsBdryX[x]with x=0 . . . upsBdrySize−1.

The upsampling boundary samples upsBdryX[x] with x=0 . . . upsBdrySize−1are derived as follows:

-   -   If needUpsBdryX is equal to TRUE and upsBdrySize is less than        nTbX, the following applies:

uDwn=nTbX/upsBdrySize

upsBdryX[x]=refX[x*uDwn]  (8-X30)

upsBdryX[x]=(Σ_(i=0) ^(uDwn−1) refX[x*uDwn+i]+(1<<(Log 2(uDwn)−1)))>>Log2(uDwn)   (8-X31)

-   -   Otherwise (upsBdrySize is equal to nTbX), upsBdryX[x] is set        equal to refX[x].

The reduced boundary samples redX[x] with x=0 . . . boundarySize−1 arederived as follows:

-   -   If boundarySize is less than upsBdrySize nTbX, the following        applies:

bDwn=upsBdrySize nTbX/boundarySize   (8-X32)

redX[x]=(Σ_(i=0) ^(bDwn−1) upsBdryX refX[x*bDwn+i]+(1<<(Log2(bDwn)−1)))>>Log 2(bDwn)   (8-X33)

The term upsBdryX in Equation 8-X33 is deleted.

-   -   Otherwise (boundarySize is equal to upsBdrySize nTbX), redX[x]        is set equal to upsBdryX[x] refX[x].

5.4 One Example

Derive prediction samples with different precisions in differentfiltering stages in the up-sampling process in ALWIP.

Below embodiments are based on the adoptedJVET-N0217-proposal-test-CE3-4.1_v2.

8.4.4.2.X4 Specification of the Prediction Upsampling Process

Inputs to this process are:

-   -   a variable predW specifying the input block width,    -   a variable predH specifying the input block height,    -   affine linear weighted samples predLwip[x][y], with x=0 . . .        predW−1, y=0 . . . predH−1,    -   a variable nTbW specifying the transform block width,    -   a variable nTbH specifying the transform block height,    -   a variable upsBdryW specifying the upsampling boundary width,    -   a variable upsBdryH specifying the upsampling boundary height,    -   top upsampling boundary samples upsBdryT[x] with x=0 . . .        upsBdryW−1,    -   left upsampling boundary samples upsBdryL[x] with x=0 . . .        upsBdryH−1.

Outputs of this process are the predicted samples predSamples[x][y],with x=0 . . . nTbW−1, y=0 . . . nTbH−1.

The sparse predicted samples predSamples[m][n] are derived frompredLwip[x][y], with x=0 . . . predW−1, y=0 . . . predH−1 as follows:

upHor=nTbW/predW   (8-X34)

upVer=nTbH/predH   (8-X35)

predSamples[(x+1)*upHor−1][(y+1)*upVer−1]=predLwip[x][y]  (8-X36)

The top boundary samples upsBdryT[x] with x=0 . . . upsBdryW−1 areassigned to predSamples[m][−1] as follows:

predSamples[(x+1)*(nTbW/upsBdryW)−1][−1]=upsBdryT[x]  (8-X37)

The left boundary samples upsBdryL[y] with y=0 . . . upsBdryH−1 areassigned to predSamples[−1][n] as follows:

predSamples[−1][(y+1)*(nTbH/upsBdryH)−1]=upsBdryL[y]  (8-X38)

The predicted samples predSamples[x][y], with x=0 . . . nTbW−1, y=0 . .. nTbH−1 are derived as follows:

-   -   If nTbH is greater than nTbW, the following ordered steps apply:        -   1. When upHor is greater than 1, horizontal upsampling for            all sparse positions (xHor, yHor)=(m*upHor−1, n*upVer−1)            with m=0 . . . predW−1, n=1 . . . predH is applied with dX=1            . . . upHor−1 as follows:

predSamples[xHor+dX][yHor]=((upHor−dX)*predSamples[xHor][yHor]+dX*predSamples[xHor+upHor][yHor])/upHor  (8-X39)

-   -   -   2. Vertical upsampling for all sparse positions (xVer,            yVer)=(m, n*upVer−1) with m=0 . . . nTbW−1, n=0 . . .            predH−1 is applied with dY=1 . . . upVer−1 as follows:            -   If yVer is equal to −1,                predSamples[xVer][yVer]=predSamples[xVer][yVer]<<log                2(upHor)

predSamples[xVer][yVer+dY]=((upVer−dY)*predSamples[xVer][yVer]+dY*predSamples[xVer][yVer+upVer])/upVer+(1<<(log2(upHor)+log 2(upVer)−1)))>>(log 2(upHor)+log 2(upVer))   (8-X40)

-   -   Otherwise, the following ordered steps apply:        -   1. When upVer is greater than 1, vertical upsampling for all            sparse positions (xVer, yVer)=(m*upHor−1, n*upVer−1) with            m=1 . . . predW, n=0 . . . predH−1 is applied with dY=1 . .            . upVer−1 as specified in (8-X40) (8-X41).

predSamples[xVer][yVer+dY]=((upVer−dY)*predSamples[xVer][yVer]+dY*predSamples[xVer][yVer+upVer])  (8-X41)

-   -   -   2. Horizontal upsampling for all sparse positions (xHor,            yHor)=(m*upHor−1, n) with m=0 . . . predW−1, n=0 . . .            nTbH−1 is applied with dX=1 . . . upHor−1 as specified in            (8-X39) as follows.            -   If xHor is equal to −1,                predSamples[xHor][yHor]=predSamples[xHor][yHor]<<log                2(upVer)

predSamples[xHor+dX][yHor]=((upHor−dX)*predSamples[xHor][yHor]+dX*predSamples[xHor+upHor][yHor]+(1<<(log2(upHor)+log 2(upVer)−1)))>>(log 2(upHor)+log 2(upVer))   (8-X42)

5.5 Examples Corresponding to Bullet 40

Suppose the block dimensions are W×H. Samples P(x, y) with x=Sx, Sx+Kx,Sx+2Kx, Sx+3Kx, . . . , y=Sy, Sy+Ky, Sy+2Ky, Sy+3Ky . . . are input tothe up-sampling process to derive the up-sampled samples S(x, y) withx=0, 1, 2 . . . W−1, y=0, 1, 2, . . . H−1. Kx and Ky are step sizesalong the horizontal and vertical directions respectively. (Sx, Sy) isthe starting position.

Suppose 1-D up-sampling is done horizontally in the first stage and 1-Dup-sampling is done vertically in the second stage.

In one example, the output results in the first stage withoutright-shifting may be derived as

S′(Sx+Kx−1, Sy)=F1*P(Sx, Sy)+F2*P(Sx+Kx, Sy).

S′(Sx+Kx−1, Sy+Ky)=F1*P(Sx, Sy+Ky)+F2*P(Sx+Kx, Sy+Ky).

F1, F2 are coefficients for a 2-tap filter and F1+F2=2^(N).

Then an output result in the second stage may be derived as

S′(Sx+Kx−1, Sy+1)=F3*S′(Sx+Kx−1, Sy)+F4*S′(Sx+Kx−1, Sy+Ky).

F3, F4 are coefficients for a 2-tap filter and F3+F4=2^(N).

Then the final up-sampled sample value may be derived as:

S(Sx+Kx−1, Sy+1)=Shift(S′(Sx+Kx−1, Sy+1), 2N);

S(Sx+Kx−1, Sy)=Shift(S′(Sx+Kx−1, Sy), N);

S(Sx+Kx−1, Sy+Ky)=Shift(S′(Sx+Kx−1, Sy+Ky), N);

The examples described above may be incorporated in the context of themethods described below, e.g., methods 1100-1400 and 2100-2400, whichmay be implemented at a video encoder and/or decoder.

FIG. 11 shows a flowchart of an exemplary method for video processing.The method 1100 includes, at step 1110, determining that a current videoblock is coded using an affine linear weighted intra prediction (ALWIP)mode.

The method 1100 includes, at step 1120, constructing, based on thedetermining, at least a portion of a most probable mode (MPM) list forthe ALWIP mode based on an at least a portion of an MPM list for anon-ALWIP intra mode.

The method 1100 includes, at step 1130, performing, based on the MPMlist for the ALWIP mode, a conversion between the current video blockand a bitstream representation of the current video block.

In some embodiments, a size of the MPM list of the ALWIP mode isidentical to a size of the MPM list for the non-ALWIP intra mode. In anexample, the size of the MPM list of the ALWIP mode is 6.

In some embodiments, the method 1100 further comprises the step ofinserting default modes to the MPM list for the ALWIP mode. In anexample, the default modes are inserted prior to the portion of a MPMlist for the ALWIP mode that is based on the MPM list for the non-ALWIPintra mode. In another example, the default modes are insertedsubsequent to the portion of a MPM list for the ALWIP mode that is basedon the MPM list for the non-ALWIP intra mode. In yet another example,the default modes are inserted in an interleaved manner with the portionof a MPM list for the ALWIP mode that is based on the MPM list for thenon-ALWIP intra mode.

In some embodiments, constructing the MPM list for the ALWIP mode andthe MPM list for the non-ALWIP intra mode is based on one or moreneighboring blocks.

In some embodiments, constructing the MPM list for the ALWIP mode andthe MPM list for the non-ALWIP intra mode is based a height or a widthof the current video block.

In some embodiments, constructing the MPM list for the ALWIP mode isbased on a first set of parameters that is different from a second setof parameters used to construct the MPM list for the non-ALWIP intramode.

In some embodiments, the method 1100 further includes the step ofdetermining that a neighboring block of the current video block has beencoded with the ALWIP mode, and designating, in constructing the MPM listfor the non-ALWIP intra mode, the neighboring block as unavailable.

In some embodiments, the method 1100 further includes the step ofdetermining that a neighboring block of the current video block has beencoded with the non-ALWIP intra mode, and designating, in constructingthe MPM list for the ALWIP mode, the neighboring block as unavailable.

In some embodiments, the non-ALWIP intra mode is based on a normal intramode, a multiple reference line (MRL) intra prediction mode or an intrasub-partition (ISP) tool.

FIG. 12 shows a flowchart of an exemplary method for video processing.The method 1200 includes, at step 1210, determining that a lumacomponent of a current video block is coded using an affine linearweighted intra prediction (ALWIP) mode.

The method 1200 includes, at step 1220, inferring, based on thedetermining, a chroma intra mode.

The method 1200 includes, at step 1230, performing, based on the chromaintra mode, a conversion between the current video block and a bitstreamrepresentation of the current video block.

In some embodiments, the luma component covers a predetermined chromasample of the chroma component. In an example, the predetermined chromasample is a top-left sample or a center sample of the chroma component.

In some embodiments, the inferred chroma intra mode is a DM mode.

In some embodiments, the inferred chroma intra mode is the ALWIP mode.

In some embodiments, the ALWIP mode is applied to one or more chromacomponents of the current video block.

In some embodiments, different matrix or bias vectors of the ALWIP modeare applied to different color components of the current video block. Inan example, the different matrix or bias vectors are predefined jointlyfor Cb and Cr components. In another example, the Cb and Cr componentsare concatenated. In yet another example, the Cb and Cr components areinterleaved.

FIG. 13 shows a flowchart of an exemplary method for video processing.The method 1300 includes, at step 1310, determining that a current videoblock is coded using an affine linear weighted intra prediction (ALWIP)mode.

The method 1300 includes, at step 1320, performing, based on thedetermining, a conversion between the current video block and abitstream representation of the current video block.

In some embodiments, the determining is based on signaling in a sequenceparameter set (SPS), a picture parameter set (PPS), a slice header, atile group header, a tile header, a coding tree unit (CTU) row or a CTUregion.

In some embodiments, the determining is based on a height (H) or a width(W) of the current video block. In an example, W>T1 or H>T2. In anotherexample, W≥T1 or H≥T2. In yet another example, W<T1 or H<T2. In yetanother example, W≤T1 or H≤T2. In yet another example, T1=32 and T2=32.

In some embodiments, the determining is based on a height (H) or a width(W) of the current video block. In an example, W+H≤T. In anotherexample, W+H≥T. In yet another example, W×H≤T. In yet another example,W×H≥T. In yet another example, T=256.

FIG. 14 shows a flowchart of an exemplary method for video processing.The method 1400 includes, at step 1410, determining that a current videoblock is coded using a coding mode different from an affine linearweighted intra prediction (ALWIP) mode.

The method 1400 includes, at step 1420, performing, based on thedetermining, a conversion between the current video block and abitstream representation of the current video block.

In some embodiments, the coding mode is a combined intra and interprediction (CIIP) mode, and method 1400 further includes the step ofperforming a selection between the ALWIP mode and a normal intraprediction mode. In an example, performing the selection is based on anexplicit signaling in the bitstream representation of the current videoblock. In another example, performing the selection is based onpredetermined rule. In yet another example, the predetermined rulealways selects the ALWIP mode when the current video block is codedusing the CIIP mode. In yet another example, the predetermined rulealways selects the normal intra prediction mode when the current videoblock is coded using the CIIP mode.

In some embodiments, the coding mode is a cross-component linear model(CCLM) prediction mode. In an example, a downsampling procedure for theALWIP mode is based on a downsampling procedure for the CCLM predictionmode. In another example, the downsampling procedure for the ALWIP modeis based on a first set of parameters, and wherein the downsamplingprocedure for the CCLM prediction mode is based on a second set ofparameters different from the first set of parameters. In yet anotherexample, the downsampling procedure for the ALWIP mode or the CCLMprediction mode comprises at least one of a selection of downsampledpositions, a selection of downsampling filters, a rounding operation ora clipping operation.

In some embodiments, the method 1400 further includes the step ofapplying one or more of a Reduced Secondary Transform (RST), a secondarytransform, a rotation transform or a Non-Separable Secondary Transform(NSST).

In some embodiments, the method 1400 further includes the step ofapplying block-based differential pulse coded modulation (DPCM) orresidual DPCM.

In some embodiments, a video processing method includes determining,based on a rule for a current video block, a context of a flagindicative of use of affine linear weighted intra prediction (ALWIP)mode during a conversion between the current video block and a bitstreamrepresentation of the current video block, predicting, based on theALWIP mode, a plurality of sub-blocks of the current video block andperforming, based on the predicting, the conversion between the currentvideo block and a bitstream representation of the current video block.The rule may be specified implicitly using an a priori technique or maybe signaled in the coded bitstream. Other examples and aspects of thismethod are further described in items 37 and 38 in Section 4.

In some embodiments, a method for video processing includes determiningthat a current video block is coded using an affine linear weightedintra prediction (ALWIP) mode, and performing, during a conversionbetween the current video block and a bitstream representation of thecurrent video block, at least two filtering stages on samples of thecurrent video block in an upsampling process associated with the ALWIPmode, wherein a first precision of the samples in a first filteringstage of the at least two filtering stages is different from a secondprecision of the samples in a second filtering stage of the at least twofiltering stages.

In an example, the samples of the current video block are predictionsamples, intermedium samples before the upsampling process orintermedium samples after the upsampling process. In another example,the samples are upsampled in a first dimension horizontally in the firstfiltering stage, and wherein the samples are upsampled in a seconddimension vertically in the second filtering stage. In yet anotherexample, the samples are upsampled in a first dimension vertically inthe first filtering stage, and wherein the samples are upsampled in asecond dimension horizontally in the second filtering stage.

In an example, an output of the first filtering stage is right-shiftedor divided to generate a processed output, and wherein the processedoutput is an input to the second filtering stage. In another example, anoutput of the first filtering stage is left-shifted or multiplied togenerate a processed output, and wherein the processed output is aninput to the second filtering stage. Other examples and aspects of thismethod are further described in item 40 in Section 4.

6 Example Implementations of the Disclosed Technology

FIG. 15 is a block diagram of a video processing apparatus 1500. Theapparatus 1500 may be used to implement one or more of the methodsdescribed herein. The apparatus 1500 may be embodied in a smartphone,tablet, computer, Internet of Things (IoT) receiver, and so on. Theapparatus 1500 may include one or more processors 1502, one or morememories 1504 and video processing hardware 1506. The processor(s) 1502may be configured to implement one or more methods (including, but notlimited to, methods 1100-1400 and 2100-2400) described in the presentdocument. The memory (memories) 1504 may be used for storing data andcode used for implementing the methods and techniques described herein.The video processing hardware 1506 may be used to implement, in hardwarecircuitry, some techniques described in the present document.

In some embodiments, the video coding methods may be implemented usingan apparatus that is implemented on a hardware platform as describedwith respect to FIG. 15.

Some embodiments of the disclosed technology include making a decisionor determination to enable a video processing tool or mode. In anexample, when the video processing tool or mode is enabled, the encoderwill use or implement the tool or mode in the processing of a block ofvideo, but may not necessarily modify the resulting bitstream based onthe usage of the tool or mode. That is, a conversion from the block ofvideo to the bitstream representation of the video will use the videoprocessing tool or mode when it is enabled based on the decision ordetermination. In another example, when the video processing tool ormode is enabled, the decoder will process the bitstream with theknowledge that the bitstream has been modified based on the videoprocessing tool or mode. That is, a conversion from the bitstreamrepresentation of the video to the block of video will be performedusing the video processing tool or mode that was enabled based on thedecision or determination.

Some embodiments of the disclosed technology include making a decisionor determination to disable a video processing tool or mode. In anexample, when the video processing tool or mode is disabled, the encoderwill not use the tool or mode in the conversion of the block of video tothe bitstream representation of the video. In another example, when thevideo processing tool or mode is disabled, the decoder will process thebitstream with the knowledge that the bitstream has not been modifiedusing the video processing tool or mode that was disabled based on thedecision or determination.

FIG. 17 is a block diagram that illustrates an example video codingsystem 100 that may utilize the techniques of this disclosure. As shownin FIG. 17, video coding system 100 may include a source device 110 anda destination device 120. Source device 110 generates encoded video datawhich may be referred to as a video encoding device. Destination device120 may decode the encoded video data generated by source device 110which may be referred to as a video decoding device. Source device 110may include a video source 112, a video encoder 114, and an input/output(I/O) interface 116.

Video source 112 may include a source such as a video capture device, aninterface to receive video data from a video content provider, and/or acomputer graphics system for generating video data, or a combination ofsuch sources. The video data may comprise one or more pictures. Videoencoder 114 encodes the video data from video source 112 to generate abitstream. The bitstream may include a sequence of bits that form acoded representation of the video data. The bitstream may include codedpictures and associated data. The coded picture is a codedrepresentation of a picture. The associated data may include sequenceparameter sets, picture parameter sets, and other syntax structures. I/Ointerface 116 may include a modulator/demodulator (modem) and/or atransmitter. The encoded video data may be transmitted directly todestination device 120 via I/O interface 116 through network 130 a. Theencoded video data may also be stored onto a storage medium/server 130 bfor access by destination device 120.

Destination device 120 may include an I/O interface 126, a video decoder124, and a display device 122.

I/O interface 126 may include a receiver and/or a modem. I/O interface126 may acquire encoded video data from the source device 110 or thestorage medium/server 130 b. Video decoder 124 may decode the encodedvideo data. Display device 122 may display the decoded video data to auser. Display device 122 may be integrated with the destination device120, or may be external to destination device 120 which be configured tointerface with an external display device.

Video encoder 114 and video decoder 124 may operate according to a videocompression standard, such as the High Efficiency Video Coding (HEVC)standard, Versatile Video Coding (VVM) standard and other current and/orfurther standards.

FIG. 18 is a block diagram illustrating an example of video encoder 200,which may be video encoder 114 in the system 100 illustrated in FIG. 17.

Video encoder 200 may be configured to perform any or all of thetechniques of this disclosure. In the example of FIG. 18, video encoder200 includes a plurality of functional components. The techniquesdescribed in this disclosure may be shared among the various componentsof video encoder 200. In some examples, a processor may be configured toperform any or all of the techniques described in this disclosure.

The functional components of video encoder 200 may include a partitionunit 201, a predication unit 202 which may include a mode select unit203, a motion estimation unit 204, a motion compensation unit 205 and anintra prediction unit 206, a residual generation unit 207, a transformunit 208, a quantization unit 209, an inverse quantization unit 210, aninverse transform unit 211, a reconstruction unit 212, a buffer 213, andan entropy encoding unit 214.

In other examples, video encoder 200 may include more, fewer, ordifferent functional components. In an example, predication unit 202 mayinclude an intra block copy (IBC) unit. The IBC unit may performpredication in an IBC mode in which at least one reference picture is apicture where the current video block is located.

Furthermore, some components, such as motion estimation unit 204 andmotion compensation unit 205 may be highly integrated, but arerepresented in the example of FIG. 18 separately for purposes ofexplanation.

Partition unit 201 may partition a picture into one or more videoblocks. Video encoder 200 and video decoder 300 may support variousvideo block sizes.

Mode select unit 203 may select one of the coding modes, intra or inter,e.g., based on error results, and provide the resulting intra- orinter-coded block to a residual generation unit 207 to generate residualblock data and to a reconstruction unit 212 to reconstruct the encodedblock for use as a reference picture. In some example, Mode select unit203 may select a combination of intra and inter predication (CIIP) modein which the predication is based on an inter predication signal and anintra predication signal. Mode select unit 203 may also select aresolution for a motion vector (e.g., a sub-pixel or integer pixelprecision) for the block in the case of inter-predication.

To perform inter prediction on a current video block, motion estimationunit 204 may generate motion information for the current video block bycomparing one or more reference frames from buffer 213 to the currentvideo block. Motion compensation unit 205 may determine a predictedvideo block for the current video block based on the motion informationand decoded samples of pictures from buffer 213 other than the pictureassociated with the current video block.

Motion estimation unit 204 and motion compensation unit 205 may performdifferent operations for a current video block, for example, dependingon whether the current video block is in an I slice, a P slice, or a Bslice.

In some examples, motion estimation unit 204 may perform uni-directionalprediction for the current video block, and motion estimation unit 204may search reference pictures of list 0 or list 1 for a reference videoblock for the current video block. Motion estimation unit 204 may thengenerate a reference index that indicates the reference picture in list0 or list 1 that contains the reference video block and a motion vectorthat indicates a spatial displacement between the current video blockand the reference video block. Motion estimation unit 204 may output thereference index, a prediction direction indicator, and the motion vectoras the motion information of the current video block. Motioncompensation unit 205 may generate the predicted video block of thecurrent block based on the reference video block indicated by the motioninformation of the current video block.

In other examples, motion estimation unit 204 may perform bi-directionalprediction for the current video block, motion estimation unit 204 maysearch the reference pictures in list 0 for a reference video block forthe current video block and may also search the reference pictures inlist 1 for another reference video block for the current video block.Motion estimation unit 204 may then generate reference indexes thatindicate the reference pictures in list 0 and list 1 containing thereference video blocks and motion vectors that indicate spatialdisplacements between the reference video blocks and the current videoblock. Motion estimation unit 204 may output the reference indexes andthe motion vectors of the current video block as the motion informationof the current video block. Motion compensation unit 205 may generatethe predicted video block of the current video block based on thereference video blocks indicated by the motion information of thecurrent video block.

In some examples, motion estimation unit 204 may output a full set ofmotion information for decoding processing of a decoder.

In some examples, motion estimation unit 204 may do not output a fullset of motion information for the current video. Rather, motionestimation unit 204 may signal the motion information of the currentvideo block with reference to the motion information of another videoblock. For example, motion estimation unit 204 may determine that themotion information of the current video block is sufficiently similar tothe motion information of a neighboring video block.

In one example, motion estimation unit 204 may indicate, in a syntaxstructure associated with the current video block, a value thatindicates to the video decoder 300 that the current video block has thesame motion information as the another video block.

In another example, motion estimation unit 204 may identify, in a syntaxstructure associated with the current video block, another video blockand a motion vector difference (MVD). The motion vector differenceindicates a difference between the motion vector of the current videoblock and the motion vector of the indicated video block. The videodecoder 300 may use the motion vector of the indicated video block andthe motion vector difference to determine the motion vector of thecurrent video block.

As discussed above, video encoder 200 may predictively signal the motionvector. Two examples of predictive signaling techniques that may beimplemented by video encoder 200 include advanced motion vectorpredication (AMVP) and merge mode signaling.

Intra prediction unit 206 may perform intra prediction on the currentvideo block. When intra prediction unit 206 performs intra prediction onthe current video block, intra prediction unit 206 may generateprediction data for the current video block based on decoded samples ofother video blocks in the same picture. The prediction data for thecurrent video block may include a predicted video block and varioussyntax elements.

Residual generation unit 207 may generate residual data for the currentvideo block by subtracting (e.g., indicated by the minus sign) thepredicted video block(s) of the current video block from the currentvideo block. The residual data of the current video block may includeresidual video blocks that correspond to different sample components ofthe samples in the current video block.

In other examples, there may be no residual data for the current videoblock for the current video block, for example in a skip mode, andresidual generation unit 207 may not perform the subtracting operation.

Transform processing unit 208 may generate one or more transformcoefficient video blocks for the current video block by applying one ormore transforms to a residual video block associated with the currentvideo block.

After transform processing unit 208 generates a transform coefficientvideo block associated with the current video block, quantization unit209 may quantize the transform coefficient video block associated withthe current video block based on one or more quantization parameter (QP)values associated with the current video block.

Inverse quantization unit 210 and inverse transform unit 211 may applyinverse quantization and inverse transforms to the transform coefficientvideo block, respectively, to reconstruct a residual video block fromthe transform coefficient video block. Reconstruction unit 212 may addthe reconstructed residual video block to corresponding samples from oneor more predicted video blocks generated by the predication unit 202 toproduce a reconstructed video block associated with the current blockfor storage in the buffer 213.

After reconstruction unit 212 reconstructs the video block, loopfiltering operation may be performed reduce video blocking artifacts inthe video block.

Entropy encoding unit 214 may receive data from other functionalcomponents of the video encoder 200. When entropy encoding unit 214receives the data, entropy encoding unit 214 may perform one or moreentropy encoding operations to generate entropy encoded data and outputa bitstream that includes the entropy encoded data.

FIG. 19 is a block diagram illustrating an example of video decoder 300which may be video decoder 114 in the system 100 illustrated in FIG. 17.

The video decoder 300 may be configured to perform any or all of thetechniques of this disclosure. In the example of FIG. 19, the videodecoder 300 includes a plurality of functional components. Thetechniques described in this disclosure may be shared among the variouscomponents of the video decoder 300. In some examples, a processor maybe configured to perform any or all of the techniques described in thisdisclosure.

In the example of FIG. 19, video decoder 300 includes an entropydecoding unit 301, a motion compensation unit 302, an intra predictionunit 303, an inverse quantization unit 304, an inverse transformationunit 305, and a reconstruction unit 306 and a buffer 307. Video decoder300 may, in some examples, perform a decoding pass generally reciprocalto the encoding pass described with respect to video encoder 200 (FIG.18).

Entropy decoding unit 301 may retrieve an encoded bitstream. The encodedbitstream may include entropy coded video data (e.g., encoded blocks ofvideo data). Entropy decoding unit 301 may decode the entropy codedvideo data, and from the entropy decoded video data, motion compensationunit 302 may determine motion information including motion vectors,motion vector precision, reference picture list indexes, and othermotion information. Motion compensation unit 302 may, for example,determine such information by performing the AMVP and merge mode.

Motion compensation unit 302 may produce motion compensated blocks,possibly performing interpolation based on interpolation filters.Identifiers for interpolation filters to be used with sub-pixelprecision may be included in the syntax elements.

Motion compensation unit 302 may use interpolation filters as used byvideo encoder 20 during encoding of the video block to calculateinterpolated values for sub-integer pixels of a reference block. Motioncompensation unit 302 may determine the interpolation filters used byvideo encoder 200 according to received syntax information and use theinterpolation filters to produce predictive blocks.

Motion compensation unit 302 may uses some of the syntax information todetermine sizes of blocks used to encode frame(s) and/or slice(s) of theencoded video sequence, partition information that describes how eachmacroblock of a picture of the encoded video sequence is partitioned,modes indicating how each partition is encoded, one or more referenceframes (and reference frame lists) for each inter-encoded block, andother information to decode the encoded video sequence.

Intra prediction unit 303 may use intra prediction modes for examplereceived in the bitstream to form a prediction block from spatiallyadjacent blocks. Inverse quantization unit 303 inverse quantizes, i.e.,de-quantizes, the quantized video block coefficients provided in thebitstream and decoded by entropy decoding unit 301. Inverse transformunit 303 applies an inverse transform.

Reconstruction unit 306 may sum the residual blocks with thecorresponding prediction blocks generated by motion compensation unit202 or intra-prediction unit 303 to form decoded blocks. If desired, adeblocking filter may also be applied to filter the decoded blocks inorder to remove blockiness artifacts. The decoded video blocks are thenstored in buffer 307, which provides reference blocks for subsequentmotion compensation/intra predication and also produces decoded videofor presentation on a display device.

FIG. 20 is a block diagram showing an example video processing system2000 in which various techniques disclosed herein may be implemented.Various implementations may include some or all of the components of thesystem 2000. The system 2000 may include input 2002 for receiving videocontent. The video content may be received in a raw or uncompressedformat, e.g., 8 or 10 bit multi-component pixel values, or may be in acompressed or encoded format. The input 2002 may represent a networkinterface, a peripheral bus interface, or a storage interface. Examplesof network interface include wired interfaces such as Ethernet, passiveoptical network (PON), etc. and wireless interfaces such as Wi-Fi orcellular interfaces.

The system 2000 may include a coding component 2004 that may implementthe various coding or encoding methods described in the presentdocument. The coding component 2004 may reduce the average bitrate ofvideo from the input 2002 to the output of the coding component 2004 toproduce a coded representation of the video. The coding techniques aretherefore sometimes called video compression or video transcodingtechniques. The output of the coding component 2004 may be eitherstored, or transmitted via a communication connected, as represented bythe component 2006. The stored or communicated bitstream (or coded)representation of the video received at the input 2002 may be used bythe component 2008 for generating pixel values or displayable video thatis sent to a display interface 2010. The process of generatinguser-viewable video from the bitstream representation is sometimescalled video decompression. Furthermore, while certain video processingoperations are referred to as “coding” operations or tools, it will beappreciated that the coding tools or operations are used at an encoderand corresponding decoding tools or operations that reverse the resultsof the coding will be performed by a decoder.

Examples of a peripheral bus interface or a display interface mayinclude universal serial bus (USB) or high definition multimediainterface (HDMI) or Displayport, and so on. Examples of storageinterfaces include SATA (serial advanced technology attachment), PCI,IDE interface, and the like. The techniques described in the presentdocument may be embodied in various electronic devices such as mobilephones, laptops, smartphones or other devices that are capable ofperforming digital data processing and/or video display.

In some embodiments, the ALWIP mode or the MIP mode is used to compute aprediction block of the current video block by performing, on previouslycoded samples of the video, a boundary downsampling operation (or anaveraging operation), followed by a matrix vector multiplicationoperation, and selectively (or optionally) followed by an upsamplingoperation (or a linear interpolation operation). In some embodiments,the ALWIP mode or the MIP mode is used to compute a prediction block ofthe current video block by performing, on previously coded samples ofthe video, a boundary downsampling operation (or an averaging operation)and followed by a matrix vector multiplication operation. In someembodiments, the ALWIP mode or the MIP mode can also perform anupsampling operation (or a linear interpolation operation) afterperforming the matrix vector multiplication operation.

FIG. 21 describes an example method 2100 for a matrix-based intraprediction. Operation 2102 includes performing a conversion between acurrent video block of a video and a bitstream representation of thecurrent video block using a matrix based intra prediction (MIP) mode inwhich a prediction block of the current video block is determined byperforming, on reference boundary samples located to a left of thecurrent video block and located to a top of the current video block, aboundary downsampling operation, followed by a matrix vectormultiplication operation, and selectively followed by an upsamplingoperation, where instead of reduced boundary samples calculated from thereference boundary samples of the current video block in the boundarydownsampling operation, the reference boundary samples are directly usedfor a prediction process in the upsampling operation.

In some embodiments for method 2100, the reference boundary sampleslocated at positions associated with the upsampling boundary samples ofthe current video block are directly used for the prediction process inthe upsampling operation. In some embodiments for method 2100,upsampling boundary samples are not computed by averaging multipleadjacent reference boundary samples. In some embodiments for method2100, the reduced boundary samples are calculated from the referenceboundary samples of the current video block and a downscaling factor. Insome embodiments for method 2100, the boundary downsampling operationincludes a one-stage boundary sample downsampling operation. In someembodiments for method 2100, the downscaling factor is calculated by atransform block size and a downsampled boundary size.

FIG. 22 describes an example method 2200 for a matrix-based intraprediction. Operation 2202 includes performing, during a conversionbetween a current video block of a video and a bitstream representationof the current video block, at least two filtering stages on samples ofthe current video block in an upsampling operation associated with amatrix based intra prediction (MIP) mode in which a prediction block ofthe current video block is determined by performing, on previously codedsamples of the video, a boundary downsampling operation, followed by amatrix vector multiplication operation, and selectively followed by theupsampling operation, where a first precision of the samples in a firstfiltering stage of the at least two filtering stages is different from asecond precision of the samples in a second filtering stage of the atleast two filtering stages. Operation 2204 includes performing theconversion between the current video block and the bitstreamrepresentation of the current video block.

In some embodiments for method 2200, the samples of the current videoblock are prediction samples, intermediate samples before the upsamplingoperation, or intermediate samples after the upsampling operation. Insome embodiments for method 2200, the samples are upsampled in a firstdimension horizontally in the first filtering stage, the samples areupsampled in a second dimension vertically in the second filteringstage, and the first filtering stage precedes the second filteringstage. In some embodiments for method 2200, the samples are upsampled ina first dimension vertically in the first filtering stage, the samplesare upsampled in a second dimension horizontally in the second filteringstage, and the first filtering stage precedes the second filteringstage.

In some embodiments for method 2200, output upsampling results of thefirst filtering stage provides input samples to the second filteringstage, and the first filtering stage excludes performing aright-shifting operation or a dividing operation on the samples. In someembodiments for method 2200, a final up-sampled result is obtained byright-shifting by a variable Shift1 or dividing by a variable Dem1 theinput samples of the second filtering stage. In some embodiments formethod 2200, a final up-sampled result is obtained by right-shifting bya variable Shift2 or by dividing by a variable Dem2 output upsamplingresults of the first filtering stage. In some embodiments for method2200, the variable Shift1=2×the variable Shift2, and wherein thevariable Dem1=the variable Dem2×the variable Dem2. In some embodimentsfor method 2200, at least some of the samples of the current video blockare left shifted by a variable Shift3 or multiplied by a variable Dem3before being sent to the second filtering stage, and the at least someof the samples are not output upsampling results of the first filteringstage. In some embodiments for method 2200, the variable Shift3=thevariable Shift1, and wherein the variable Dem3=the variable Dem2.

In some embodiments for method 2200, output upsampling results of thefirst filtering stage is right-shifted by a variable Shift1 or dividedby a variable Dem1 to generate a processed output, and the processedoutput provides input samples to the second filtering stage. In someembodiments for method 2200, a final up-sampled result is obtained byright-shifting by a variable Shift2 or dividing by a variable Dem2 theinput samples of the second filtering stage. In some embodiments formethod 2200, the variable Shift2 is not equal to the variable Shift1 andthe variable Dem2 is not equal to the variable Dem1. In some embodimentsfor method 2200, the variable Shift2 is greater than the variable Shift1and the variable Dem2 is greater than the variable Dem1. In someembodiments for method 2200, a final up-sampled result is obtained byright-shifting by a variable Shift3 or dividing by a variable Dem3 theoutput upsampling filtering results of the first filtering stage. Insome embodiments for method 2200, the variable Shift3 is equal to thevariable Shift1, and wherein the variable Dem3 is not equal to thevariable Dem1.

In some embodiments for method 2200, the variable Shift3=the variableShift1+the variable Shift2. In some embodiments for method 2200, atleast some of the samples of the current video block are left shifted ormultiplied before being sent to the second filtering stage, and the atleast some of the samples are not the output upsampling results of thefirst filtering stage. In some embodiments for method 2200, outputupsampling results of the first filtering stage is left-shifted by avariable Shift1 or multiplied or a variable Dem1 to generate a processedoutput, and the processed output provides input samples to the secondfiltering stage. In some embodiments for method 2200, a final up-sampledresult is obtained by right-shifting by a factor or by dividing by thefactor the input samples of the second filtering stage.

In some embodiments for method 2200, a final up-sampled result isobtained by right-shifting by a factor or by dividing by the factor theoutput upsampling filtering results of the first filtering stage. Insome embodiments for method 2200, at least some of the samples of thecurrent video block are left shifted by a variable Shift2 or multipliedby a variable Dem2 before being sent to the second filtering stage, andthe at least some of the samples are not the output upsampling resultsof the first filtering stage. In some embodiments for method 2200, thevariable Shift2 is not equal to the variable Shift1, and wherein thevariable Dem2 is not equal to the variable Dem1. In some embodiments formethod 2200, the variable Shift2 is greater than the variable Shift1 andthe variable Dem2 is greater than the variable Dem1.

In some embodiments for method 2200, the samples that are input to thefirst filtering stage are left-shifted by a variable Shift1 ormultiplied by a variable Dem1 to generate a processed output, and theprocessed output provides input samples to the second filtering stage.In some embodiments for method 2200, a final up-sampled result isobtained by right-shifting by a factor or by dividing by the factor theinput samples of the second filtering stage. In some embodiments formethod 2200, a final up-sampled result is obtained by right-shifting bya factor or by dividing by the factor the processed output of the firstfiltering stage. In some embodiments for method 2200, at least some ofthe samples of the current video block are left shifted by a variableShift2 or multiplied by a variable Dem2 before being sent to the secondfiltering stage, and the at least some of the samples are not outputupsampling results of the first filtering stage. In some embodiments formethod 2200, the variable Shift2 is not equal to the variable Shift1,and wherein the variable Dem2 is not equal to the variable Dem1. In someembodiments for method 2200, the variable Shift2 is greater than thevariable Shift1 and the variable Dem2 is greater than the variable Dem1.

FIG. 23 describes an example video encoding method 2300 for amatrix-based intra prediction. Operation 2302 includes encoding acurrent video block of a video using a matrix intra prediction (MIP)mode in which a prediction block of the current video block isdetermined by performing, on previously coded samples of the video, aboundary downsampling operation, followed by a matrix vectormultiplication operation, and selectively followed by an upsamplingoperation. Operation 2304 includes adding, to a coded representation ofthe current video block, a syntax element indicative of applicability ofthe MIP mode to the current video block using arithmetic coding in whicha context for the syntax element is derived based on a rule.

FIG. 24 describes an example video decoding method 2400 for amatrix-based intra prediction. Operation 2402 parsing a codedrepresentation of a video comprising a current video block for a syntaxelement indicating whether the current video block is coded using amatrix intra prediction (MIP) mode, wherein the syntax element is codedusing arithmetic coding in which a context for the syntax element isderived based on a rule. Operation 2404 includes decoding the codedrepresentation of the current video block to generate a decoded currentvideo block, wherein in a case that the current video block is codedusing the MIP mode, the decoding includes determining a prediction blockof the current video block by performing, on previously coded samples ofthe video, a boundary downsampling operation, followed by a matrixvector multiplication operation, and selectively followed by anupsampling operation.

In some embodiments for method(s) 2300 and/or 2400, the rule definesthat the context for the syntax element is derived in response to(Abs(Log 2(cbWidth)−Log 2(cbHeight)) being greater than 1, whereincbWidth is a width of the current video block, and wherein cbHeight is aheight of the current video block. In some embodiments for method(s)2300 and/or 2400, the rule defines that the context of the syntaxelement is derived in response to (Abs(Log 2(cbWidth)−Log 2(cbHeight))being less than 1, wherein cbWidth is a width of the current videoblock, and wherein cbHeight is a height of the current video block. Insome embodiments for method(s) 2300 and/or 2400, the rule specifies thatthe context for the syntax element is derived by using the MIP moderelated information of one or more neighboring video blocks of thecurrent video block and/or availability of the one or more neighboringvideo blocks.

In some embodiments for method(s) 2300 and/or 2400, the context for thesyntax element is derived based on: a first MIP syntax element of a leftneighboring video block of the current video block, a second MIP syntaxelement of a top neighboring video block of the current video block, andan availability of the left neighboring video block and the topneighboring video block. In some embodiments for method(s) 2300 and/or2400, the context (offset ctxInc) is derived based on a followingequation: offset ctxInc=(condL && availableL)+(condA &&availableA)+ctxSetIdx*3, wherein condL is a first MIP syntax element ofa left neighboring video block of the current video block, wherein condAis a second MIP syntax element of a top neighboring video block of thecurrent video block, wherein availableL and availableA indicate anavailability of the left neighboring video block and the top neighboringvideo block, respectively, wherein && indicates a logical And operation,and wherein ctxSetIdx is a predefined context index.

In some embodiments for method(s) 2300 and/or 2400, context is derivedbased on: a MIP syntax element of a left neighboring video block of thecurrent video block, and an availability of the left neighboring videoblock. In some embodiments for method(s) 2300 and/or 2400, the context(offset ctxInc) is derived based on a following equation: offsetctxInc=(condL && availableL)+ctxSetIdx*3, wherein condL is the MIPsyntax element of the left neighboring video block of the current videoblock, wherein availableL indicate an availability of the leftneighboring video block, wherein && indicates a logical And operation,and wherein ctxSetIdx is a predefined context index.

In some embodiments for method(s) 2300 and/or 2400, context is derivedbased on: a MIP syntax element of a top neighboring video block of thecurrent video block, and an availability of the top neighboring videoblock. In some embodiments for method(s) 2300 and/or 2400, the context(offset ctxInc) is derived based on a following equation: offsetctxInc=(condA && availableA)+ctxSetIdx*3, wherein condA is the MIPsyntax element of the top neighboring video block of the current videoblock, wherein availableA indicate an availability of the topneighboring video block, wherein && indicates a logical And operation,and wherein ctxSetIdx is a predefined context index. In some embodimentsfor method(s) 2300 and/or 2400, the predefined context index ctxSetIdxis equal to zero. In some embodiments for method(s) 2300 and/or 2400,the rule specifies that the context for the syntax element is one fixedcontext with which the syntax element is coded using the arithmeticcoding. In some embodiments for method(s) 2300 and/or 2400, the rulespecifies that the syntax element is bypass coded using the arithmeticcoding.

In some embodiments for method(s) 2300 and/or 2400, the rule specifiesthat the context is derived from K contexts, where K is greater than orequal to 2. In some embodiments for method(s) 2300 and/or 2400, a firstcontext in an order from the K contexts is used in response to W>N*H orH>N*W, and wherein N is 2. In some embodiments for method(s) 2300 and/or2400, a second context in an order from the K contexts is used inresponse to W≤N*H or H≤N*W, and wherein N is 2. In some embodiments formethod(s) 2300 and/or 2400, the rule specifies that the context isderived from N other contexts, where N is greater than or equal to zero.In some embodiments for method(s) 2300 and/or 2400, N is equal to 3, thecontext for the syntax element is derived by using two MIP syntaxelements of two video blocks and/or availability of the two videoblocks, and the two video blocks are two neighboring video blocks of thecurrent video block or the two video blocks are two non-adjacent videoblocks of the current video block.

In some embodiments for method(s) 2300 and/or 2400, the two neighboringvideo blocks include a top neighboring video block relative to thecurrent video block and a left neighboring video block relative to thecurrent video block. In some embodiments for method(s) 2300 and/or 2400,the top neighboring video block covers a position (x0, y0−1) and theleft neighboring video block covers a position (x0−1, y0), wherein aluma location (x0, y0) specifies a top-left sample of the current videoblock. In some embodiments for method(s) 2300 and/or 2400, the twoneighboring video blocks include a top neighboring video block relativeto the current video block and a below-left neighboring video blockrelative to the current video block. In some embodiments for method(s)2300 and/or 2400, the two neighboring video blocks include a topneighboring video block relative to the current video block and atop-right neighboring video block relative to the current video block.In some embodiments for method(s) 2300 and/or 2400, the two neighboringvideo blocks include a top-right neighboring video block relative to thecurrent video block and a left neighboring video block relative to thecurrent video block.

In some embodiments for method(s) 2300 and/or 2400, the two neighboringvideo blocks include a top-right neighboring video block relative to thecurrent video block and a below-left neighboring video block relative tothe current video block. In some embodiments for method(s) 2300 and/or2400, the two neighboring video blocks include a left neighboring videoblock relative to the current video block and a below-left neighboringvideo block relative to the current video block. In some embodiments formethod(s) 2300 and/or 2400, the two neighboring video blocks include anytwo of: a top-right neighboring video block relative to the currentvideo block, a top neighboring video block relative to the current videoblock, a top-left neighboring video block relative to the current videoblock, a left neighboring video block relative to the current videoblock, and a below-left neighboring video block relative to the currentvideo block.

In some embodiments for method(s) 2300 and/or 2400, N is equal to 2, thecontext for the syntax element is derived by using one MIP syntaxelement of one video block and/or availability of the one video block,and the one video block is a neighboring video block of the currentvideo block or the one video block is a non-adjacent video block of thecurrent video block. In some embodiments for method(s) 2300 and/or 2400,the one neighboring video block include any one of: a top-rightneighboring video block relative to the current video block, a topneighboring video block relative to the current video block, a top-leftneighboring video block relative to the current video block, a leftneighboring video block relative to the current video block, and abelow-left neighboring video block relative to the current video block.In some embodiments for method(s) 2300 and/or 2400, the rule specifiesthat the context for the syntax element is one fixed context with whichthe syntax element is coded using the arithmetic coding. In someembodiments for method(s) 2300 and/or 2400, the rule specifies that thesyntax element is bypass coded using the arithmetic coding.

From the foregoing, it will be appreciated that specific embodiments ofthe presently disclosed technology have been described herein forpurposes of illustration, but that various modifications may be madewithout deviating from the scope of the invention. Accordingly, thepresently disclosed technology is not limited except as by the appendedclaims.

Implementations of the subject matter and the functional operationsdescribed in this patent document can be implemented in various systems,digital electronic circuitry, or in computer software, firmware, orhardware, including the structures disclosed in this specification andtheir structural equivalents, or in combinations of one or more of them.Implementations of the subject matter described in this specificationcan be implemented as one or more computer program products, i.e., oneor more modules of computer program instructions encoded on a tangibleand non-transitory computer readable medium for execution by, or tocontrol the operation of, data processing apparatus. The computerreadable medium can be a machine-readable storage device, amachine-readable storage substrate, a memory device, a composition ofmatter effecting a machine-readable propagated signal, or a combinationof one or more of them. The term “data processing unit” or “dataprocessing apparatus” encompasses all apparatus, devices, and machinesfor processing data, including by way of example a programmableprocessor, a computer, or multiple processors or computers. Theapparatus can include, in addition to hardware, code that creates anexecution environment for the computer program in question, e.g., codethat constitutes processor firmware, a protocol stack, a databasemanagement system, an operating system, or a combination of one or moreof them.

A computer program (also known as a program, software, softwareapplication, script, or code) can be written in any form of programminglanguage, including compiled or interpreted languages, and it can bedeployed in any form, including as a stand-alone program or as a module,component, subroutine, or other unit suitable for use in a computingenvironment. A computer program does not necessarily correspond to afile in a file system. A program can be stored in a portion of a filethat holds other programs or data (e.g., one or more scripts stored in amarkup language document), in a single file dedicated to the program inquestion, or in multiple coordinated files (e.g., files that store oneor more modules, sub programs, or portions of code). A computer programcan be deployed to be executed on one computer or on multiple computersthat are located at one site or distributed across multiple sites andinterconnected by a communication network.

The processes and logic flows described in this specification can beperformed by one or more programmable processors executing one or morecomputer programs to perform functions by operating on input data andgenerating output. The processes and logic flows can also be performedby, and apparatus can also be implemented as, special purpose logiccircuitry, e.g., an FPGA (field programmable gate array) or an ASIC(application specific integrated circuit).

Processors suitable for the execution of a computer program include, byway of example, both general and special purpose microprocessors, andany one or more processors of any kind of digital computer. Generally, aprocessor will receive instructions and data from a read only memory ora random access memory or both. The essential elements of a computer area processor for performing instructions and one or more memory devicesfor storing instructions and data. Generally, a computer will alsoinclude, or be operatively coupled to receive data from or transfer datato, or both, one or more mass storage devices for storing data, e.g.,magnetic, magneto optical disks, or optical disks. However, a computerneed not have such devices. Computer readable media suitable for storingcomputer program instructions and data include all forms of nonvolatilememory, media and memory devices, including by way of examplesemiconductor memory devices, e.g., EPROM, EEPROM, and flash memorydevices. The processor and the memory can be supplemented by, orincorporated in, special purpose logic circuitry.

It is intended that the specification, together with the drawings, beconsidered exemplary only, where exemplary means an example. As usedherein, the use of “or” is intended to include “and/or”, unless thecontext clearly indicates otherwise.

While this patent document contains many specifics, these should not beconstrued as limitations on the scope of any invention or of what may beclaimed, but rather as descriptions of features that may be specific toparticular embodiments of particular inventions. Certain features thatare described in this patent document in the context of separateembodiments can also be implemented in combination in a singleembodiment. Conversely, various features that are described in thecontext of a single embodiment can also be implemented in multipleembodiments separately or in any suitable subcombination. Moreover,although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination can in some cases be excised from thecombination, and the claimed combination may be directed to asubcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. Moreover, the separation of various system components in theembodiments described in this patent document should not be understoodas requiring such separation in all embodiments.

Only a few implementations and examples are described and otherimplementations, enhancements and variations can be made based on whatis described and illustrated in this patent document.

What is claimed is:
 1. A method of processing video data, comprising: determining, for a conversion between a video block of a video and the bitstream of the video, that a first intra mode is applied on the video block of the video, wherein process in the first intra mode includes a one-stage boundary downsampling operation, followed by a matrix vector multiplication operation and an upsampling operation to generate prediction samples for the video block of the video; and performing the conversion based on the prediction samples; wherein reduced boundary samples are generated from reference boundary samples of the video block of the video by the one-stage boundary downsampling operation and are used to generate inputs to the matrix vector multiplication operation.
 2. The method of claim 1, wherein the reference boundary samples include left and above reference boundary samples of the video block.
 3. The method of claim 2, wherein the left and above reference boundary samples are derived without an intra reference sample filtering process.
 4. The method of claim 2, wherein in the one-stage boundary downsampling operation, the reduced boundary samples are generated directly from the reference boundary samples of the video block and a downscaling factor without deriving intermediate samples, and wherein the downscaling factor is calculated only once for a horizontal direction and a vertical direction, respectively.
 5. The method of claim 4, wherein the downscaling factor is calculated based on a size of the video block.
 6. The method of claim 1, wherein inputting samples to the upsampling operation include upsampling boundary samples of the video block, and the upsampling boundary samples are not computed by averaging the reference boundary samples of the video block.
 7. The method of claim 6, wherein at least one of the upsampling boundary samples are copied from the reference boundary samples.
 8. The method of claim 1, wherein a first syntax element indicating whether to apply the first intra mode is included in the bitstream.
 9. The method of claim 1, wherein the matrix vector multiplication operation is followed by a transposing operation prior to the upsampling operation.
 10. The method of claim 9, wherein the transposing operation converts a block having a width of a first value and a height of a second value to a block having the width of the second value and a height of the first value.
 11. The method of claim 1, wherein the conversion includes encoding the video block into the bitstream.
 12. The method of claim 1, wherein the conversion includes decoding the video block from the bitstream.
 13. An apparatus for processing video data comprising a processor and a non-transitory memory with instructions thereon, wherein the instructions upon execution by the processor, cause the processor to: determine, for a conversion between a video block of a video and the bitstream of the video, that a first intra mode is applied on the video block of the video, wherein process in the first intra mode includes a one-stage boundary downsampling operation, followed by a matrix vector multiplication operation and an upsampling operation to generate prediction samples for the video block of the video; and perform the conversion based on the prediction samples; wherein reduced boundary samples are generated from reference boundary samples of the video block of the video by the one-stage boundary downsampling operation and are used to generate inputs to the matrix vector multiplication operation.
 14. The apparatus of claim 13, wherein the reference boundary samples include left and above reference boundary samples of the video block derived without an intra reference sample filtering process.
 15. The apparatus of claim 14, wherein in the one-stage boundary downsampling operation, the reduced boundary samples are generated directly from the reference boundary samples of the video block and a downscaling factor without deriving intermediate samples, and wherein the downscaling factor is calculated only once for a horizontal direction and a vertical direction, respectively.
 16. The apparatus of claim 15, wherein the downscaling factor is calculated based on a size of the video block.
 17. The apparatus of claim 13, wherein inputting samples to the upsampling operation include upsampling boundary samples of the video block, wherein at least one of the upsampling boundary samples are copied from the reference boundary samples.
 18. The apparatus of claim 13, wherein inputting samples to the upsampling operation include upsampling boundary samples of the video block, and the upsampling boundary samples are not computed by averaging the reference boundary samples of the video block.
 19. A non-transitory computer-readable storage medium storing instructions that cause a processor to: determine, for a conversion between a video block of a video and the bitstream of the video, that a first intra mode is applied on the video block of the video, wherein process in the first intra mode includes a one-stage boundary downsampling operation, followed by a matrix vector multiplication operation and an upsampling operation to generate prediction samples for the video block of the video; and perform the conversion based on the prediction samples; wherein reduced samples are generated from reference boundary samples of the video block of the video by the one-stage boundary downsampling operation and are used to generate inputs to the matrix vector multiplication operation.
 20. A non-transitory computer-readable recording medium storing a bitstream of a video which is generated by a method performed by a video processing apparatus, wherein the method comprises: determining, that a first intra mode is applied on the video block of the video, wherein process in the first intra mode includes a one-stage boundary downsampling operation, followed by a matrix vector multiplication operation and an upsampling operation to generate prediction samples for the video block of the video; generating the bitstream based on the determining; and wherein reduced samples are generated from reference boundary samples of the video block of the video by the one-stage boundary downsampling operation and are used to generate inputs to the matrix vector multiplication operation. 